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Amphibole Supergroup, part I
Posted by Olav Revheim
Olav Revheim October 01, 2010 01:32PMThis article has been prepared for the Mindat Best Minerals project. The aim of this project is to present information on important localities and specimens for each mineral specie. As new finds are made and new knowledge is made available the individual articles will be revised to include this information. Readers are encouraged to contribute by posting a response in this thread. All revisions will be stored, thus ensuring traceability and availability of previously included information. A complete list of articles can be found in the list of finished Best Minerals articles. To cite this version: Revheim, O. (2012) Amphibole Supergroup Part I. revision 1.0. Mindat Best Minerals Project, article "mesg-66-197996". Please be advised that the photos cannot be used without the consent of the copyright holder
Amphibole Supergroup, Part I
The amphibole group minerals have been given a separate “best minerals” article due to the immense complexity of the group. Altogether, there are more than 100 individual amphibole minerals that can often be quite difficult to separate. On a general basis there are many more similarities between the different minerals in this group than differences.
It is not possible to write on amphiboles without touching into chemistry, as it is the unique design of the amphibole molecule that creates the diversity of different minerals that is practically speaking indistinguishable for most collectors. The basis of the amphibole molecule is double rings of SiO4 groups creating a base structure of 8 Silicon atoms and 22 Oxygen atoms. These rings are stacked on top of each other creating long, double chains, responsible for the elongation of the crystals along the c-axis, hence the term "double chain silicates".
In between these rings there are small voids that can be filled with other ion-groups. It is these double rings, plus the ions that fills the open voids in the structure that gives the general amphibole formula of:
Where the A, B and C positions can be filled with various ions of the right size to fill the open space. The T position is normally filled with Si and Al in various ratios (Si>Al), and the W position is normally filled with (OH), but also F,Cl and O may fill this position.
For a “normal” mineral group, there will be restrictions on the allowable electrical charge for the ions filling these open voids in addition to the size restrictions. This is not so much the case with the amphibole structure. In this structure, the A position can be vacant (charge zero) or filled with large ions with a single positive charge like Na or K, or even a 2+ charge like Ca. The same is valid from the B position, where the positive charge varies from 2 (i.e. Na2) to 4 (i.e Ca2), and the C position from 10+(i.eMg5) to 13+ (ieMg2FeTi).
As the structure itself must be balanced, the balance is made up by substituting up to 3 of the 8 Si atoms in the chain structure with Al, increasing the negative charge from the Si8O22 double rings from 14- to 11-. (In addition, the (OH)2 groups can be substituted with O2 or other ions).
This causes a wide variety of possible chemical formulas to fit into the same structure, creating minerals with very different chemical composition, but similar crystal structure, physical properties and visual appearance. This complexity creates a headache for anyone wanting to classify or accurately name an amphibole. It does not help that most amphiboles are of intermediate composition between multiple mineral species. For more details on how the various amphibole minerals is related, see the Mindat article Amphibole supergroup minerals and their relationship
The amphibole supergroup is according to the newest nomenclature organized into two groups in accordance with the content in the W position:
The w(OH,F,Cl)-dominant Amphibole group and the wO dominant subgroup. The latter group containing as pr. 2012 only a handful of minerals. The w(OH,F,Cl)-dominant Amphibole group contains 8 subgroups, based on the content in the B position. These groups are:
Subgroup I: Mg-Fe-Mn Amphibole SubgroupSubgroup II: Calcium Amphibole SubgroupSubgroup III: Sodium-Calcium Amphibole SubgroupSubgroup IV: Sodium Amphibole SubgroupSubgroup V: Lithium Amphibole SubgroupSubgroup VI: Sodium Mg-Fe-Mn Amphibole SubgroupSubgroup VII: Lithium Mg-Fe-Mn Amphibole SubgroupSubgroup VIII: Lithium-Calcium Amphibole Subgroup
Each sub-group is further divided into Root-name groups, based on the elements in the C position. The individual minerals within each series are defined by the dominant content in the A and C positions or if F2, Cl2 substitutes for OH. Unfortunately, the division into root-name groups for many amphiboles arbitrary as there is fully interchangeability between them.
This new (2012) supergroup-group-subgroup-root name group- species hierarchy is only valid for monoclinic amphiboles, not taking into account the orthorhombic amphiboles, such as anthophyllite and gedrite. In theory these amphiboles could be placed anywhere in the hierarchy, but in this text I have placed them at the "Root name Group" level.
The classification of amphiboles in this article is based on Oberti et. al (2012) amphibole classification, which is a major change in how amphiboles are classified, but it is still built upon work presented by Leake (1978) and the numerous later revisions. Leake published a completely new classification system for the amphiboles. Prior to this, amphiboles were classified by a number of features, including color, optical properties, minor elements, locations etc. It appears to me that Leake made three drastic changes:
1) He applied the 50% rule and distinguished all amphiboles based on chemistry (and crystal system) alone, and also set a standard for how to present the chemical formula.
2) He set subgroups and made charts for how the various amphiboles should relate to each other
3) He obsoleted over 200 amphibole names, and (re)defined a lot of the others.
The benefits of this are obviously a structured system with given boundaries between the individual minerals where these boundaries have been set according to predefined rules. As a result it became possible to assign one and only one name to an amphibole of a given composition.
The drawback is and will always be that the amphiboles are a complex group of minerals that are not easily classified. In addition, obsolete and re-defined mineral names are not necessarily synonymous with only one of the "new" amphibole names but often two or three. The underlying complexity of this group will still be intact, no matter how it is classified, and I doubt that we have seen the final attempt in classifying this mineral group.
In the following text, the various amphibole root-name groups are presented under their subgroup heading. Each amphibole specie belonging to a root-name group is listed. It should be noted though that many of the listed mineral species are either Named ( i.e. found in nature but not approved) or Hypothetical ( i.e described, but not found in nature). It is impossible to give an accurate account of all the amphibole species found in nature.
Note that the various amphibole-root-name groups written in blue text are linked to a more detailed "best of" article for the specific root-name group. The amphiboles that do not have a separate "best of" article are too rare and obscure to produce specimens from more than a handful of localities, and then often only as rims on crystals or small grains in the host rock. They are "never" the dominant amphibole in their host rocks and are impossible to accurately identify, except by a very few mineralogists.
Subgroup I contains minerals with Mg, Fe, Mn in the B position. There is full interchangeability between Mg, Fe and Mn in the B position, with the Mg amphiboles being more common.
Although not in alignment with the latest nomenclature, I have let this subgroup contain amphiboles with both monoclinic (cummingtonite-grunerite root-name groups) and orthorhombic ( anthophyllite-gedrite root-name group) symmetry. For the clino-amphoiboles, all the SiO4 tetrahedrons are oriented in the same direction, whereas for the orthoamphiboles, the SiO4 tetrahedrons next to each other are oriented in opposite directions, thus giving different crystal symmetry. The Protoamphiboles are still orthorhombic in their symmetry, but with the alternating SiO4 tetrahedrons arranged in pairs, thus giving a unit cell dimension only half that of their orthorhombic polymorphs.
The Mg,Fe,Mn amphiboles are mainly minerals found in metamorphic rocks, enriched in Mg,Fe and Mn respectively. Cummingtonite is often found in conjunction with ore bodies, but also in some Mg-rich schists/gneisses. Grunerite is most frequently found in metamorphic banded iron formations.
Anthophyllite is common in metamorphic ultramafic rocks and in Mg/Al rich gneisses with gedrite. The colors of these minerals normally range from whitish through beige and browns towards black. The light colored ones are often mistaken for tremolite. There are no way to distinguish these minerals based their physical appearance.
None of these specimens form great specimens; the most spectacular must be the iridescent Gedrite-Anthophyllite crystals from Risør, Norway and the "Hermanov balls" from the Czech Republic. Other than that, star-shaped aggregates and fibrous masses are probably the most collectable specimens.
I.1 Cummingtonite-root name group
The cummingtonite minerals are the Mg dominant end member in a continuous solid solution series with the Fe-dominant grunerite minerals, and are polymorphs to minerals in the orthorhombic anthophyllite series
Cummingtonite has not always been defined with the chemical and structural boundaries as it has now, and in particular the early literature distinguishes poorly between cummingtonite, grunerite, tremolite/actinolite and the now discredited dannemorite and tirodite. "Dannemorite" often contains sufficient Fe and Mn to fall within the grunerite boundaries, but may occasionally contain sufficient Mg to be a cummingtonite.
"Tirodite" is a discredited name for Mn-rich amphiboles that normally falls within the cummingtonite-manganocummingtonite range, and should be labeled cummingtonite-group unless a chemical analysis proves otherwise.
Like most of the amphiboles, the cummingtonite minerals are not found in large, well-formed and colorful crystals. It is normally found as beige, greenish or brownish fibrous or bladed aggregates. From the locations with photographed specimens in the Mindat database, the cummingtonite from Mina de Moro in Brazil and from the localities near the type locality at Cummington, USA appears to be the best.
Cummingtonite is, as grunerite, often found in banded iron formations, although in the amphibole Fe content in or near the iron ore itself will normally give a grunerite-series mineral. Cummingtonite may also be found in other stratabound metasedimentary ore formations ( Manganese, Zinc) in addition to some conventional Ca,Na and Al poor schists and gneisses. It may also be found in some eruptive rocks. Cummingtonite is as pr. feb 2012 listed at 261 localities in Mindat.
Manganocummingtonite is almost exclusively found with metamorphic manganese ore. It often occurs with rhodonite, spessartine and cummingtonite. At least some of the 38 manganocummingtonite localities listed in Mindat (Feb 2012) are probably manganoan cummingtonite with a too low Mn content to qualify as manganocummingtonite. Manganocummingtonite as a name will be discredited in the near future, and be grouped together with manganogruenerite in a new Mn-dominant root-name group
I.2 Grunerite-root-name group
The grunerite amphiboles form the Fe-rich members in a continuous series with cummingtonite and manganocummingtonite.
Grunerite and manganogrunerite are quite common in Precambrian banded iron formations (BIF) when these are metamorphosed to amphibolite facies. In these cases grunerite is a rock forming mineral and can be found throughout large areas, such as the Labrador and Lake Superior areas of North America, in Australia and in Sweden together with other iron minerals such as magnetite, Fe-carbonates ( siderite) and various iron silicates, often also near chert or jasper. Manganogrunerite occurs in the same areas and same geological environments, when these environments are enriched in manganese. Since grunerite-series amphiboles is found together with minerals of economic interest, they will be analyzed and identified more often than more common amphiboles not found in deposits of economic interest.
Grunerite-series minerals normally occur as small shiny fibers in the rock, but can occasionally form crystalline mats or stars. The dm-long fibrous aggregates from Penge in South Africa are rather unique, but will never form especially attractive mineral specimens. These asbestos-like fibrous aggregates are called amosite, and this is often considered a synonym or variety of grunerite. This is not exactly the case, as the name amosite has also been used for riebeckite found in the same geological province.
Dannemorite is an old name for manganoan grunerite that has been used as an synonym for manganogrunerite, and even in some recent texts, the name dannemorite are used. Even though dannemorite are used when the grunerite contains some Mn, it does not always contain sufficient amounts to qualify as manganogrunerite.
Grunerite are described from 165 localities in Mindat, and are predominantly found in metamorphic iron formations (BIF) in the contact between the iron ore and silica rich rocks. It can occur as a rock-forming mineral in formations covering large areas some places.
Manganogrunerite is described from 70 localities in Mindat, normally associated with manganiferous iron ore together with grunerite. It is unclear whether all of them contain sufficient manganese to qualify as manganogrunerite.
Manganogrunerite as a name will be discredited in the near future, and be grouped together with manganocummingtonite in a new Mn-dominant root-name group
Hypothetical end member- will probably be discredited as it no longer has a value as an end member in a series.
I.5 Anthophyllite-root-name group
Anthophyllite is an amphibole with an orthorhombic crystal structure. The basic building block of the anthophyllite will still be the same amphibole SiO4 double chains as for its monoclinic polymorph cummingonite. The relationship between the anthophyllite series, tremolite/actinolite and the cummingtonite-series is complex.
Anthophyllite minerals appears to be the preferred minerals in environments with a steep H2O or temperature gradient; hence it’s common occurrence in shear zones or as Heřmanovské balls. They are minerals found in metamorphic rocks, predominantly meta-pyroxenites or –peridotites as well as Mg-rich carbonate rocks.
Anthophyllite minerals does not form well developed crystals, but rather fibrous crystalline masses that can exceed multiple tons in weight and several m3 in volume. The mineral specimens are not particularly interesting for collectors. The most attractive specimens seems to be the "Hermanov balls" from the Czech Republic, where anthophyllite forms radiating fibers around globular biotite/phlogopite aggregates. The largest masses seem to have occurred in Paakkila, Finland and Pelham, Massachusetts, USA where anthophyllite was mined as asbestos.
Anthophyllite is listed from 514 localities ( Oct 2011) at Mindat and it occurs most frequently in metamorphosed ultramafic olivine/pyroxene rock together with talc, chlorite, tremolite/actinolite and other Mg-rich minerals. It also occurs with gedrite and cordierite in some Mg-rich gneiss.
Ferroanthophyllite is a very rare amphibole, listed from 4 localities (Oct 2011) in the Mindat database. It seems to be most frequently associated with ore deposits.
This is a rare amphibole, listed from 3 localities(Oct 2011) from metamorphosed ultramafic rocks in Mindat
This is a rare amphibole, listed from 2 localities (Oct 2011) in metamorphosed ultramafic rocks in Mindat, also associated with pegmatites.
This is a rare amphibole, listed from 2 localities(Oct 2011) associated w/ manganese mineralization in chert.
Hypotethical end member
Hypothetical end member
I.6 Gedrite- root name group
The gedrite series minerals form a continuous series with the anthophyllite series of minerals with two chemical substitutions dominating:
1: (Mg,Fe)Si -- AlAl and
2: Si -- NaAl
There is a full solid solution series along these substitutions, and the divide between the two series are arbitrarily set to AlSi7 in the T position. This divide deviates from the principles used to classify the monoclinic amphiboles, and should be revised. Minerals in the anthophyllite and gedrite root-name groups is therefore often referred to as members of the "anthophyllite-gedrite" series, not taking into consideration the Mg/Fe ratio or Na content.
The gedrite-series minerals can be considered the Al-rich end-members in this series, although silica deficient gedrites (Si<6,0 apfu) are known from nature, and sodic-ferrogedrite and sodic-gedrite from 2 and 1 localities respectively.
It is virtually impossible to distinguish the gedrite minerals from the more common anthophyllite, which also occurs in the same type of environments. It is not made easier when chemical analysis of a large number of samples “shows that orthoamphiboles termed anthophyllites by one author overlap with gedrites of other authors and vice-versa.” Beeson 1978. Gedrite can obviously also be confused with other amphiboles.
The star formed fans from the Bergslagen ore-district in Sweden are about as attractive an amphibole gets in a metamorphic rock. Also some of the orthoamphiboles (anthophyllite-gedrite series) from the Bamble formation can be quite attractive, for an amphibole that is.
Ferrogedrite are listed from 10 localitites having roughly the same, although more ferrous, geologic environment as gedrite.
Gedrite occurs in metamorphic rocks, most commonly in amphibolites and gneisses together with other Mg/Al minerals such as other amphiboles, cordierite, sapphirine, phlogopite and plagioclase feldspars or with kyanite. It can also occur in more Fe-rich environments together with biotite, staurolite and almandine. Gedrite is by far the most common of the gedrite series minerals ( 122 localities in mindat pr. feb-2012)
Sodic-ferrogedrite are listed from 2 localities (feb 2012) in Mindat, and are consequently a very rare mineral. The Fe2+ content increases the stability field of the mineral, and the two localities listed in mindat seems to be correct even with the redefinition of the mineral.
Sodicgedrite are listed from 1 locality in Mindat (Feb 2012), and even if it i known from some other localities as well, it is still a rare mineral. It ios used as an indicator of UHP metamorphosis in granulite facies rocks.
The Calcium amphibole subgroup is the largest amphibole sub-group with somewhere between 30-40 acknowledged minerals. Some of them are also amongst the most common amphiboles. There is some dispute on the number of calcium amphiboles that has actually been found and the numbers presented above are to the best of my knowledge, and should not be considered authorative on the matter.
The calcium amphibole subgroup is characterized by containing two Ca 2+ ions in the B position. The minerals in this sub-group form a continuous series with otherwise similar minerals in subgroup III Sodium-Calcium amphiboles. The various series within the Calcium amphibole subgroup are primarily distinguished based on their covalence number in the C position.
This subgroup contains common rock-forming minerals such as actinolite, pargasite and similar as well as very rare minerals only found in one or very few locations worldwide, and the calcium amphiboles are formed when the pressure/temperature regime meets the amphibole stability area and sufficient Ca and H2O is present to favor their formation. These conditions are found in a wide range of rocks, both igneous and metamorphic. The best crystals are found in metamorphic limestones ( marbles/ calc-silicate rocks and skarns) as well as phenocrysts or microcrystals in volcanic rocks. Although common in metagabbros and metabasalts and other amphibolites, these rocks do not necessarily produce brilliant crystals.
The probably best and most interesting locations for calcium amphiboles can be found in marbles and skarns in New York, USA and Ontario, Canada where igneous rocks of varying composition have penetrated a horizon of marbles during the Grenville Orogeny. During metamorphosis to amphibolite facies a wide range of amphiboles, some of them unique to this area, has been formed in the contact between the marble and the igneous rocks.
Something similar has happened during the Himalayan orogeny, where some of the most attractive amphibole specimens have formed together with rubies and spinels during metamorphosis of clay-bearing marbles. This inaccessible area obviously has a great potential for finding new amphiboles.
The Central European Volcanism offers a different, and possibly even richer, environment for calcium amphiboles as magmas of various compositions has penetrated a continental crust containing a wide variety of rocks. Most of the amphiboles are formed as beautiful micro-crystals in ejectas and xenolites from the volcanoes, but embedded phenocrysts in the lavas are also known. These embedded amphiboles often have a high O/OH ratio, and there is a potential of identifying new O dominant amphiboles from these rocks
II.1 Cannilloite root-name group
This series contains only cannilloite and fluorcannilloite, of which only the latter has been found in nature, and then in only one (as pr. 2010) confirmed locality, namely the type locality in Pargas, Finland. The relatively spectacular green amphiboles found at Luc Yen, Vietnam is pargasite, and not fluorcannilloite as claimed. See http://www.mindat.org/mesg-7-69925.html and http://www.mindat.org/mesg-7-198029.html.
In a strict mineralogical sense, this is a very interesting series at it is the only amphibole where the A position filled with a 2+ ion, Ca, but that alone doesn't make the mm sized grains in the Pargas marble any display-worthy specimens.
II.2 Tremolite - Actinolite-ferroactinolite series
This series contans the following minerals:
Tremolite is a common mineral in metamorphosed dolomite rocks and other iron-poor calc-silicate rocks. It can also be found in metamorphosed peridotites and other Mg rich rocks. There are currently (august 2011) more than 1700 locations listed in Mindat. The best crystals seems to come from Africa (Tanzania,Kenya and Madagascar) and North America ( Canada, USA). Normally any pale amphibole from a calc-silicate rock will be named tremolite, whether correct or not.
Fluortremolite (Named amphibolel)
Fluortremolite is closely related to tremolite, except that F substitutes for OH. A few localities (5 as pr feb 2012) are listed in Mindat, but it doesn't seem as all of them qualifies as fluortremolite with F>OH, although two of the New York locations seems to qualify as fluortremolite proper. ( ref: Marian Lupulescu (2008): Amphibole Group Minerals from New York State. Rocks & Minerals, Volum,e 83 May/June.). One of these fluorotremolites probably contains sufficient iron to qualify as fluoroactinolite.
In Parvo-manganotremolite Mn substitutes for Ca in the B position, and it is described from 1 locality (Arnold Mine in New York, USA) where it is found most often as rims on parvo-mangano edenite. This is a mineral name that will be abolished in the new 2012 amphibole nomenclature
Actinolite is in all practical aspects an iron bearing variety of tremolite with an IMA approved mineral name in its own right. It contains some Fe substituting for Mg at the C-site. It is a common mineral, listed from more than 2500 locations (august 2011) and can be found in the following environments:
1. Contact metamorphic localities and skarn
2. Regional metamorphic localities
3. Alpine type veins
4. Miarolitic cavities in granites and other igneous rocks
Ferro-actinolite has more Fe than Mg in the C position, and is predominantly found in iron rich calc-silica rock. The mineral is probably more common that the few locations (78 as pr. october 2010) listed in Mindat. The best crystal pictured in the Mindat galleries is from Pakistan, but similar crystals are also named ferropargasite, and neither seems to be backed up by analytical data.
II.3 Magnesiohornblende root-name group
Hornblende is used as a field term for many dark amphiboles (mostly belonging to the calcium and sodium-calcium subgroups), Consequently almost any amphibole found that is not sufficiently spectacular or important to be properly analyzed will be named hornblende. This is exemplified in that when searching in the Rruff database for hornblende, there will be 13 hits ( as of oct. 2010), Of the 13 you will find 3 edenites, 4 pargasites and 6 hastingsites, but no magnesiohornblende or ferrohornblende.
Magnesiohornblende is probably a lot more common than the approximately 150 (Oct 2010) locality listings in the Mindat database. There are remarkably few photos uploaded of this mineral, but both the localities in Japan and Norway has produced good crystals and crystal groups.
Despite having more than 230 localities listed (Oct 2010) in the Mindat database, ferrohornblende still should be more common than the number of listings indicates. There are some great microcrystals from Italy in the photo gallery ( The ones from the Montenenero quarry has been identified as magnesiohornblende), and also some nice crystals from Sweden.
Fluormagnesiohornblende is a mineral that is not approved by IMA, even if it has been found in Coal Mine no 45 in Kopeisk, Southern Ural, Russia. This mineral has formed in the extreme conditions of a coal fire, and since these normally are a result of human activity, IMA has decided not to approve minerals formed this way.
In many older collections ( in particular in museums), good specimens are displayed and named hornblende, since that is what it was at the time. The name hornblende is still accepted by IMA and petrologists as any aluminous calcium amphibole of unknown composition, but it is not a valid mineral name.
II.4 Tschermakite root name group
The tschermakite-root name group of minerals is a series of rock forming minerals not known in specimens attractive to collectors. Tschermakite can be found in a wide range of geological environments, and in the 44 entries in Mindat includes calc-silicate rocks, sulphide ores, gabbroes, volcanic rocks as well as 3 meteorites. An extended literature search in petrographic and mineralogical literature would undoubtedly yield several tschermakite localities not currently included in the Mindat database, but since these minerals are rock-forming minerals, not all of them would qualify as a mineral occurrence from a collector's point of view. Many of the localities for Tschermakite minerals listed in Mindat lacks a proper reference and only one of the photos are from a referenced location. Some of the hypothetical end-members may be known from nature, but not (yet) been given a sufficiently comprehensive description to be approved.
Tschermakite has been redefined in the 2012 amphibole nomenclature. The chemistry of the various tschermakite specimens should therefore be revisited to verify its new identity.
Tschernakite is the most common of the minerals in the series. It is found in a wide range of geological environments, and is more common than indicated in Mindat.
The majority of the locations are in sulphide bearing greenschists and skarns. The latter often in conjunction with tonalites or other silica-poor igneous rocks. The link between ferrotschermakite and sulphides is, I think, mostly due to the higher probability of interest in mineral localities with an economic potential.
Hypotetical end member.
Hypotetical end member.
II.5 Edenite root name group
Edenite is one of the classic amphibole minerals, first described from Edenville, New York USA in 1839. The Edenville locality is one of the many great amphibole localities in New York and Ontario in the marbles and contact rocks formed during the Grenville orogeny. Large and well-formed edenites are found here, although many of the classic edenites has proven to be pargasite or other amphiboles rather than an edenite mineral. Even at the type locality the occurrence of edenite has been questioned ( Handbook of mineralogy).
The edenite molecule (magnesium end member) is unstable and pure edenite has not been found in nature, and it has even been impossible to make synthetic. (Oberti et all. 2006). It has been found that Fe and F stabilizes the edenite molecule and any edenite found in nature will always contain some Fe and/or F . Ferroedenite and fluoroedenite are more stable and more common than edenite.
The edenite minerals are primarily found in marbles and calc-silicate/skarn rocks and as microcrystals in volcanic rocks. It can also be found in the alkali rocks in Russia and Norway.
Edenite is found in skarns and calc-silicate rocks and as a late forming mineral in vugs in some volcanic rocks, and the largest crystals can be found in New York, USA and Ontario, Canada. It should be noted that all edenite contains F and/or Fe, and many specimens labeled edenite in reality are fluoredenite or ferroedenite. It is quite probable that some of the more than 100 (aug 2011) edenite localities listed in the database in reality should be ferro- or fluoroedenite.
Ferroedeinte are found in the same type of environments as edenite, and also in some alkaline complexes. It, probably incorrectly, appears to be rarer than edenite with its close to 40 listed localities.
Fluoroedenite occurs in the same type of environments as ferroedenite, and is the most stable and most common of the edenite minerals, but is only listed from 25 localities. Many of the edenite localities on the US east coast are probably also carry fluoroedenites. Beautiful fluoroedenite microcrystals are known from some European localities ( Italy, France and Germany).
Found together with parvo-manganotremolite in a mangenese-rich pod in a talc/tremolite rock in the Arnold Mine in New York, USA. This is a mineral name that will be abolished in the new 2012 amphibole nomenclature
Chloropotassic Ferroedenite- NOT IMA Approved
Found in a calc-silicate rock in the Willroy mine, Manitouwadge mining Camp, Ontario, Canada.
II.6 Pargasite root name group
The pargasite minerals are of intermediate composition compared to the other calcium-amphiboles, and solid solution series exists to several other calcium amphibole group. Often more than one amphibole is present at the given locality, and it may also be difficult to accurately identify the amphibole species. In many cases the literature references states something like "amphibole of tschermakitic or pargasitic composition".
The largest, well-formed crystals of pargasite are known from calc-silicate rocks and marbles at Pargas, Finland as well as New York,USA, whereas the most attractive specimens will be the intense green, sometimes gemmy pargasite from the ruby bearing marbles of Pakistan, Burma and Vietnam.
Hypotetical end member.
Ferropargasite is most frequently found in Fe-rich skarns and calc-silicate rocks. Of the 35 localities ( Sept. 2011) listed on Mindat, the seemingly best crystals are those found at Keene, New York, USA.
Many of the US and Finnish pargasites contains significant amounts of F, and many localities undoubtedly carry both fluoropargasite and pargasite. Fluoropargasite is probably more common than the 4 localities currently listed in the Mindat database.
Fluoro-potassicpargasite was IMA approved in 2010 ( IMA No. 2009-091), and the type locality Tranomaro area, Fort Dauphini region, Madagascar are still (?) the only location. A 5mm crystal from the original find is pictured at rruff.info.
Pargasite is a common rock forming mineral and are found in a wide variety of geological environments. It is listed from 240 localities ( Sept. 2011) in Mindat and large, well-formed crystals are known from Pargas, Finland, New York, USA and Ontario Canada. Spectacular transparent green crystals are found in Pakistan and Vietnam.
Potassic-Pargasite are listed from 6 localities in Mindat. 5 of these are from the Grenville orogeny marbles in New York USA and Pargas, Finland. It is difficult to say how common this mineral really is, but it has been found in large (multiple cm) well-formed crystals.
Potassic-ferropargasite is a rare mineral ( 3 entries in the Mindat database as pr. Sept. 2011) found in potassium enriched calc-silicate rocks.
Cl-analogue of Ferropargasite
This is still (Sept. 2011) not an approved mineral, but it has been found in an ultrabasic intrusion at one locality in Canada.
Ehimeite is the only amphibole with Cr as a dominant ion, and it has been described from Mount Higashi-Akaishiyama, Ehime Prefecture, Japan. Ehimeite will probably, according to the newest nomenclature be renamed as chlorio-pargasite.
II.7 Hastingsite root name group
The Hastingsite-series minerals are characterized by having four (Mg,Fe) atoms and one Al atom in the C position and ferric iron rather than Al as trivalent ions in the C-positions. Identifying the Fe3+/Fe2+ is paramount for the identification of a hastingsite-series mineral, as the chemical composition is very near the pargasites, the edenites and others.
All minerals in this root name group, except hastingsite and magnesiohastingsite are very rare, with 5 or less localities listed in the Mindat database.
This mineral has been listed from 5 localities in the Mindat database, and is found in various chlorine rich metamorphic rocks and dunite. It was first described from an epidote/magnetite skarn at Dashkesan, Azerbijan.
This mineral is listed from two localities in the Mindat database, with the micro-crystals found in andesine xenoliths at Oroi hill, Romania as the most prolific.
New York, Orange County, Greenwood Mine
This mineral is known from only one locality in New York, USA, where it occurs as lustrous cleavages up to 2cm size in a banded compact massive magnetite ore hosted in amphibolite gneiss. (The amphiboles in the host rock are other species.) There are no vugs with free-growing crystals, just massive ore, although some bands do reach very coarse almost pegmatitic textures. In addition to fluorine, this amphibole is quite enriched in chlorine, compared to most other amphiboles.
Hastingsite is relatively common, but collectible specimens are almost exclusively found with magnetite ore, most often in skarn rocks. It also occurs as a rock forming mineral in acidic igneous rocks. The largest and best crystals seem to have come from Franklin Hill in the US. It is listed from almost 150 localities worldwide in the Mindat database,
Magnesiohastingsite is found in several different environments, ranging from skarns, volcanic rocks and alkali rocks and 60 localities are listed in the Mindat database ( sept 2011). The presence of ferric iron is necessary for this mineral to form. Again, Franklin Hill seems to have produced the best specimens, although it is difficult to identify to the older material with any confidence. The Langesundfjord, Norway crystal is also outstanding, as is the Italian micro's.
This mineral is known from a biotite amphibole gabbro together with other amphiboles at the Ilmen Natural reserve in Russia.
Potassichastingsite - NOT IMA Approved
This is not an approved mineral, but is listed from 4 localities in the Mindat database (sept 2011). It occurs in skarns and alkaligranites.
II.9 Sadanagaite-root name group
All of the sadanagaite minerals are very rare minerals with only one or two locations listed in the Mindat database. An extensive search in petrological and mineralogical literature will undoubtedly increase the number of locations, but these minerals will still be very rare. The largest crystals seem to be the 1mm long prismatic crystals embedded in vesuvianite at the Yuge Limestone quarry in Japan.
The sadanagaite minerals have been found in different geological environments, but most frequently (always?) associated with other calc-silicate minerals in metamorphic rock and always in extremely silica poor environments. The approved sadanagite minerals are as follows:
- - - - -
Joesmithite is a very rare amphibole found only in Långban, Sweden. It has formed in the contact between a late Be bearing pegmatite and Pb bearing ore. Joesmithite is placed in the calcium subgroup at a root name level, but given the weird chemistry, additional minerals with a joesmithite root name will be surprising.
These amphiboles have an intermediate composition between the calcium-subgroup and the sodium-subgroup. They are most common in alkaline igneous rocks and carbonatites. Some of the rarer calcium-sodium amphiboles are also found as retrograde minerals in ecglogite or blueschist facies metamorphic rocks.
Richterite root-name group
The richterite minerals are the most common series in the Sodium-Calcium Subgroup. Richterite is an end-member root name and they are a characteristic mineral in some alkaline rocks, such as lamproites, kimberlites and the like. It is in these rocks that richterites occurs most frequently, but most often as minute grains in the rock groundmass, and of very little interest for the average collector. These minerals also occur with arfvedsonite in carbonatites, but also here most frequently as small grains in the rock.
World-wide, there are only three occurrences that produces display specimens, Ontario Canada, Koksha Afghanistan and the Kedrovyi alkaline Massif Russia. These three areas produce some of the most spectacular amphiboles that can be found, whether it is the up to 30cm long, doubly terminated black crystals from Ontario, the transparent golden richterites from Afghanistan or the blue jade-like material from Russia.
The richterite minerals form intermediate members both within the series, towards other amphiboles in the sodium-calcium subgroup (winchite root name group) and towards the calcium subgroup ( tremolite and edenite root name groups) and the sodium subgroup (arfvedsonite-root name group). Many of the amphiboles found at the localities included in this text are such intermediate members, and some of the pictured specimens may not be the described richterite species.
22 localities in Mindat (april 2012)
10 localities in Mindat (april 2012)
18 localities on Mindat (april 2012)
18 localities on Mindat (April 2012)
2 localities on Mindat (April 2012)
104 localities on mindat (April 2012)
III.2 Winchite root name group
The winchite minerals have an intermediate composition between the tremolite-actinolite series and the glaucophane-root name group minerals. It should be noted that the definition of the mineral does not entirely fit with its chemical formula. Given its intermediate composition, its rarity and somewhat unclear definition it seems possible to discredit all of the minerals in this root-name group without this being a big loss. That being said, the winchite series minerals are approved minerals that has been identified from several localities and they deserve a place in any systematic collection.
The winchite minerals are in the somewhat self-contradicting position of being both more common and rarer than originally believed. It is more common as rims and zones in multi-zoned amphiboles in many rocks from multiple worldwide localities, but it is rarer as a collectible mineral than we mineral collectors would like to think.
The yellowish, transparent amphiboles from the Koksha valley in Afghanistan has been marketed as winchite, but the few analysis that has been made on this material indicates that these amphiboles are richterite minerals rather than winchite.
The manganoan cummingtonites of Talcville New York is often named parvowinchite. This incorrect naming is based on a misunderstanding of the name tirodite. Several analysis is made on this material and both the Al content and Na content is way too low for these amphiboles to be anything else than a Mn-rich cummingtonite. ( It should be noted that the most common amphiboles from Talcville are tremolite and anthophyllite). It is also difficult to see how the geological environment at this locality could support an alkali-rich amphibole.
The known, confirmed occurrences of winchite are all from multi-amphibole environments, and unless accompanied with a confirmed analysis of the exact same material, the identification of a mineral as winchite will always be tentative, possibly speculative.
☐ (NaCa) (Fe2+4Fe3+)Si8O22(OH)2
☐ (NaCa) (Mg4Fe3+)Si8O22(OH)2
☐ (NaCa) (Fe2+4Al)Si8O22(OH)2
☐( NaMn2+) (Mg4Al)Si8O22(OH)2This is a mineral name that will be abolished in the new 2012 amphibole nomenclature
☐( NaCa) (Mg4Al)Si8O22(OH)2
III.3 Katophorite root name group
The katophorite minerals are intermediate in composition between the richterite minerals and the taramite minerals and between the edenite-minerals and arfvedsonite minerals, and may be found together with minerals from these series. It should also be realized that for all of katophorite minerals listed here, only ferrokatophorite and katophorite are formally approved by IMA, all the others are in the "Named" category
Katophorite minerals are normally found in alkaline intrusions, such as nepheline syenites and also lamproites and similar rocks, typically together with other Sodium and Calcium bearing amphiboles. The Khibina massif in Russia is infamous in this respect, as 25 different amphiboles have been identified there.
The best katophorite crystals are those from the Bear Lake diggings in Ontario, Canada, where giant, well-formed crystals exceeding a foot in length can be found in the calcite vein-dykes. It should be noted that also here more than one amphibole-series is present, and some of the (fluoro)katophorites from Bear Lake will undoubtedly be richterites or even edenites.
The Norwegian katophorites from the Larvik plutonic complex is also quite good for an amphibole.
Na(NaCa)(Fe2+4 Fe3+) (Si7Al) O22(OH)2
Listed from 4 localities in Mindat, all in alkaline massifs (Sept 2012)
Na(NaCa)(Mg4 Al) (Si7Al) O22F2
Listed from 3 localities in Mindat, The Bear Lake diggings in Ontario Canada where large fluor-kataphorite crystals occur with richterite in calcite vein-dykes are the most prominent.
Na(NaCa)(Fe2+4 Al) (Si7Al) O22(OH)2
Listed from 34 localities in Mindat, predominantly from alkaline intrusives, but also in partly retrograde metamorphic rocks as an intermediate member between glaucophane and calcium amphiboles.
Na(NaCa)(Mg4 Fe3+) (Si7Al) O22(OH)2
Listed from 7 localities in Mindat, predominantly from alkaline intrusives.
Na(NaCa)(Mg4 Al) (Si7Al) O22(OH)2
Listed from 26 localities in Mindat, predominantly from alkaline intrusives, but also from carbonatites and from the Bear Lake diggings.
Unnamed (K-analogue of ferrikatophorite)
K(NaCa)(Mg4 Fe3+) (Si7Al) O22(OH)2
Listed from only one locality in the Khibiny Massif in Russia
The barroisite minerals are all very rare minerals, with ferrobarroisite as the most common of them ( 38 localities april 2012). The barroisite minerals' chemical composition is intermediate between Al-rich calcic amphiboles such as pargasite/tschermakite and glaucophane. The barroisite minerals occur in high pressure/medium temperature metamorphic rocks, typically eclogies and amphibolites, but never as the major consistuent of these rocks, and always together with other amphiboles. It will therefore normally be necessary to analyse a specimen to verify if any barroisite is present.
The barroisite minerals is probably more common than the very few locations listed on mindat will indicate, but normally as small grains or zones of small grains in the rocks where they occur.
Barroisite has been redefined in the latest (2012) nomenclature, and the chemistry of the various barroisite specimens must be verified to give a correct ID.
Hypotetical end member
The taramite series minerals are rare minerals, normally occurring together with other, more common amphiboles, and a specimen should not be labeled taramite unless there is some clear evidence that the specimen really contains taramite. Taramite is most frequently found in alkali-rocks, such as nepheline syenites. In some rare cases, taramite is the dominant amphibole in mariupolite, a type of nepheline syenite found in the Mariuplo massif in Ukraine and a handful of other places. The taramites from nepheline syenite always has a very high Fe/Mg ratio, and prior to discovering magnesiotaramite in retrograde eclogite(s) it was speculated that a high Fe ratio was necessary for taramite to form.
The photo above is from the magnesiotaramite type locality and may well contain magnesiotaramite, but if so associated with other amphiboles. The type description of the material was made from grains too small to measure the specific gravity of the material, and it is unlikely that a 4 cm magnesiotaramite aggregate would have remained unnoticed by the scientists working on the occurrence.
Taramite has been redefined in the latest (2012) nomenclature, and the chemistry of the various taramite specimens must be verified to give a correct ID.
Hypotetical end member
1 locality (March 2012)
Click here to view Best Minerals A, and here for Best Minerals A to Z and here for Fast Navigation for finished Best Minerals articles.
Edited 75 time(s). Last edit at 12/14/2015 06:46PM by Olav Revheim.
Rock Currier October 03, 2010 01:47AMOlav,
You have really started it! Congratulations. I went in and tweaked the pictures a little and installed the captions. I changed your float=right to float=center which works better when you are tweaking your pictures and fiddled the pixel sizes a little to get them to come out more the same size and moved a couple of pictures around to make it a bit more artistic. Harjo made me do it.
Crystals not pistols.
Rock Currier July 07, 2011 12:20PMOlav,
I have been reviewing a number of the best minerals articles and I think for consistency that on your images in this article, you should clearly indicate where each of the specimens come from. I know that the user can click on the image and read the full locality off of the full size image, but I don't think we want to make them go to that much trouble.
Crystals not pistols.
Rock Currier September 04, 2011 09:03PMOlav,
I noticed that some of the pictures the frame is larger than the pictures. You can often increase the size of the image to make it fit the frame. In some cases like the Potassicsadanagaite, 12mm FOV, Ozernovskii Massif, Lake Baikal area, Eastern-Siberian Region, Russia you can shrink the frame considerably by shortening the caption. In this case you can probably remove the Eastern-Siberian Region without any harm.
Crystals not pistols.
Pavel Kartashov September 05, 2011 03:40AMDear Olav,
good beginning. But amphiboles photos selected by you are too gemmy, especially pargasite. I am think that less 0.05% of pargasite is of such color. You can to say, that this is best specimens - OK! Why in this case selected tremolite is more similar to actinolite, then actinolite itself given by you?
Chloro-potassichastingsite was first described from magnetite-epidote skarns.
Rock Currier September 05, 2011 08:36PMOlav,
I have been dinking (=futzing or making small changes) around in some of the other amphabole articles, not changing or adding content, but mostly tweaking the format to make them more in line with our standard formatting as it now exists. Some of the articles like Actinolite were done before we had more or less settled on our existing format. And Oh yes, I have always found Pavel's suggestions to be good ones and he has helped me stay out of trouble on more than one occasion.
Crystals not pistols.
Olav Revheim September 06, 2011 08:14AMRock and Pavel.
Thank you so much for your comments. It is correct that only a small fraction of the pargasites are the gemmy green variety for Pakistan and Vietnam. However, these locations are of the very few locations where specimen mining for amphiboles takes place. As a result, probably more than 50% of the pargasites offered for sale are of this type, and therefore I'd like to keep this image as is.
The tremolite-actinolite-ferroactinolite series are difficult, and I am thinking that these minerals probably should be merged into one article, as very many of the specimens are not analysed and probably of intermediate composition. It does not seem to take more than 2-3% FeO to give a greenish color to a tremolite, and the very attractive green tremolites from Merelani Hills, Tanzania are colored by V2O3. I also agree that we need to revisit the first articles we did ( actinolite, tremolite, hornblende etc.) both because we have matured the format of these articles quite a bit, and because a lot of new specimen photos has been uploaded, such as this:
I still think that I will prioritize adding new articles for a while.
Edited 1 time(s). Last edit at 09/06/2011 09:52AM by Olav Revheim.
Olav Revheim April 08, 2012 05:30PMRock,
I cannot add more text to this best of article now, as it has reached the maximum size allowed in the message board. What do you think I should do?
1) Split it into 6 entries, one for the amphibole group and one for each of the 5 subgroups?
2) Remove this text from the message board and create an article in the "Articel section" of mindat?
or something else.
Rock Currier April 08, 2012 09:20PMOlav
I think your idea for keeping the amphabole group minerals to gather is a good one and I would suggest you split it into Amphabole Group A to M and N to Z or some such. Congratulations on reaching 60K for an article. You are the first moderator to do that. We still do not know the shape of what the Best Minerals work will become.
Dave, if you see this, can you tell us how many characters are allowed in an article edit field? Also, can the number of characters for these fields be increased with out disruption to the system? Just curious, I think the fields are big enough already and can't see making users do any more scrolling than is necessary.
Crystals not pistols.
Ralph Bottrill April 09, 2012 12:42AMOlav,
This is becoming a really excellent article, well done!
I think you have the right idea, a summary amphibole page with the main divisions, and each of these divisions having their own page.
For such a complex supergroup most us us love to hate, you have done a remarkable job. However I would query some of your subdivisions, eg the cummingtonite and grunerite series. You have used these terms to describe the series with the Mn-rich endmembers, but grunerite and cummingtonite form a complete series too. It may be best to give mangaocummingtonite and manganogrunerite their own pages? I take the point that we don't know if some of these manganocummingtonites are just manganoan cummingtonite, etc but this applies to most amphibole specimens that have not been individually analyzed. The Ca-Na amphiboles are even more complex eg magnesiohornblende can form a series with actinolite, glaucophane, kaesutite, edenite, hastingsite, tschermakite, etc. and it may be best to have pages for endmembers rather than series.
The proto amphiboles like Protoanthophyllite are just polytypes not true species last I heard, and we seem to have some incorrect data in the main mineral pages eg Protoanthophyllite formula, but I will need to check all this. The IMA may be going to simplify the nomenclature sometime, eg get rid of intermediates like the winchites, but we have to go with what we have meanwhile.
Olav Revheim April 09, 2012 06:38AMRalph,
Thank you very much for your comments and feed-back.
I understand and appreciate your queries on the subdivisions. Like you say, gruenerite/ cummingtonite and the manganoan equivilents are clearly a three-dimensional series, and could possibly be merged into one series. Then you have all the other multi-dimensional series, involving not only one element, but two elements, and as you say the Na-Ca amphiboles that are forms series across the subgroups. Then you have Al-Fe3+ substitution that sometimes are delt with as for ferritschermakite and sometimes with a different root name (pargastite-hastingsite). My take on this is that whatever I do it won't be correct, so I have taken the "simple" approach and called all the amphiboles with the same root-name for a series. It is probably no the best way, and I am open for suggestions how to do it differently.
It seems to me from the IMA webpage by checking both the 2009 pdf and the recent updated xl spreadsheet (feb 2012) that protoanthophyllite for some unknown reason still is an approved mineral.
I have also noticed that many of the manganoan cummingtonites suddenly becomes manganocummingonite. I have noticed this tendency for all adjective modifiers with the same root name ( i.e potassian richterite becomes potassicrichterite all of a sudden), so I have started to be consequent in using Mn-rich or K-rich rather than managanoan and so on.
Rock Currier April 09, 2012 07:54AMOlav, Don't worry if you don't get it completely right the first time. The beauty of this kind of online format is that you can easily shift the data and their images into new configurations when it seems like the correct thing to do. It may be that Ralph's idea is better than my simplistic one. I sure won't argue against it. Perhaps a few more people will chip in with their ideas.
Crystals not pistols.
Ralph Bottrill April 10, 2012 07:24AMI was wrong on the proto amphiboles, they are still accepted, though only differing in space group, and can only be identified by careful single crystal work (sigh!).
I note in the latest review by Hawthorne and Obertti, the suggestion is to get rid of many names eg grunerite becomes ferro-cummingtonite, but I'm not sure how the wider mineralogical community feels about it all. Except for a few eccentric crystal chemists and floundering petrologists, most people run from the amphiboles!
Keep up the good work!
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