Amphibole Supergroup, Part II

First draft


Please see Amphibole Supergroup Part 1 for a description of subgroups I to III

The amphibole supergroup is according to the latest nomenclature (2012) 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 Subgroup
Subgroup II: Calcium Amphibole Subgroup
Subgroup III: Sodium-Calcium Amphibole Subgroup
Subgroup IV: Sodium Amphibole Subgroup
Subgroup V: Lithium Amphibole Subgroup
Subgroup VI: Sodium Mg-Fe-Mn Amphibole Subgroup
Subgroup VII: Lithium Mg-Fe-Mn Amphibole Subgroup
Subgroup VIII: Lithium-Calcium Amphibole Subgroup


Subgroup IV: Sodium Amphibole Subgroup

Arvfedsonite, riebeckite and glaucophane root name amphiboles are the most common of the sodium amphiboles and in particular arfvedsonite (but also riebeckite) can occur as large, well-formed crystals in cavities in alkaline pegmatites. Both arfvedsonite and riebeckite are common in alkaline igneous rocks, arvfdsonite more common in under-saturated rocks such as nepheline syenites. Glaucophane is a common mineral metamorphic rocks from subduction zones (high pressure- low temperature rocks) and is the coloring mineral of blueschists. Riebeckite in the form of asbestos has been excavated in large volumes in South Africa in particular, and is still cause of health and environmental issues decades after the mining operations ended.


Glaucophane Root name group

Glaucophane 8mm crystals	© DSW 2010

Glaucophane and Ferroglaucophane are typical minerals of high pressure, low temperature metamorphosed rocks. Such rocks are typical of subduction zones where continental and oceanic crust are pushed deep into the earth's crust relatively quickly ( in geologic terms, that is). If the subducted rocks stay deep in the crust, the P/T conditions will normalize and the glaucophane bearing rocks will be further metamorphosed to greenschist/amphibolite facies rocks, in which calcium amphiboles ( compositions from actinolite to pargasite) will be stable. Therefore, glaucophane bearing rocks found on surface is indicative of a rapid subduction into the crust and then an equally rapid return to the surface (again, rapid in geological terms). Many of the localities described here show a gradual transformation from glaucophane schists to calcium amphiboles as the main amphiboles, and in some of these rocks exotic intermediate amphiboles such as barroisites and winchites can be found.

There is a continuous series between glaucophane and ferroglaucophane, with glaucophane as the most common mineral. The glaucophane series often also has a riebeckite (sometimes also an arfvedsonite) component, thus forming a series towards riebeckite. Crossite is a discontinued name for an intermediate composition between glaucophane and riebeckite. There is also a series between glaucophane via sodic-calcic amphiboles towards calcic amphiboles of actinolitic to pargasitic composition.

Glaucphane does not form large, free standing crystals, and do not offer mineral collectors anyhing but a nice blue color.

Ferroglaucophane
[ ]Na₂(Fe₃Al₂)Si₈O₂₂(OH)₂

Ferroglaucophane is listed from 21 localities in the Mindat database. Many, if not all these localities also contains the more common glaucophane.

Glaucophane
[ ]Na₂(Mg₃Al₂)Si₈O₂₂(OH)₂

Glaucophane is listed from 235 localities in the Mindat database.


Riebeckite Root name group

Crocidolite 80x70x50mm specimen, Northern Cape Province, South Africa	©

The riebeckite minerals belongs to the sodium-amphibole subgroup, characterized by having Na₂ in the B position of the amphibole molecule. There is a continuous series between riebeckite and magnesio-ribeckite, and also between riebeckite and other amphiboles. Although riebeckite is a very common mineral (riebeckite is listed from 314 localities in Mindat and magnesioriebeckite 70), also in large crystals, good specimens are few and far between.

Riebeckite ( with Fe/Mg>>1) is a common mineral in alkaline granites and syenites. It occurs as a rock forming mineral in these rocks, and large crystals (up to and exceeding 75cm in maximum length) can be found embedded in pegmatites belonging to riebeckite containing granites. Riebeckite can also be found as free standing crystals in cavities in these granites, often then in the form of asbestiform fibres, crocidolite. These free standing crystals do not necessarily form attractive specimens.

In some of these granites, riebeckite can have a significant F content, and analysis of F dominant riebeckite has been published, thus justifying fluororiebeckite as a "named" amphibole species.

In alkaline granites and syenites, a continuous series exist between arfvedsonite and the riebeckite, and the general rule of thumb is that riebeckite is found in the more silica rich alkaline rocks, although this rule is not without exceptions. Riebeckite is also found in metamorphic rocks where it forms a continuous series towards glaucophane.

Riebeckite is stable in lower pressure and temperature environments than other amphiboles and the asbestiform variety crocidolite can be found in sedimentary banded iron formations (BIF's). The crocidolite can be found as in veins and bands in these rocks, although rarely exceeding 10 cm fiber length. In some of these environments, the rocks have undergone only low grade metamorphosis, and it has been suggested that riebeckite can form at temperatures down towards 100 deg C.

The riebeckite Fe/Mg ratio is normally lower in metamorphic rocks, and the rarer magnesioriebeckite can be found in some of these metamorphic environments.

For most of the 20th century, riebeckite asbestos ( blue asbestos, crocidolite) was mined in large mining operations in Australia, South Africa and other places, and the total production can be counted in millions of tons. This mining has been stopped due to the severe negative health effects of asbestos.


Riebeckite
Na₂ (Fe2+₃ Fe3+₂ ) Si₈ O₂₂(OH)₂

Riebeckite is listed from 314 localities in Mindat

Magnesioriebeckite
Na₂ (Mg3Fe3+₂ ) Si₈ O₂₂(OH)₂

Magnesioriebeckite is listed from 70 localities in Mindat.


Eckermannite Root name group

Eckermannite 25mm specimen, Norra Kärr, Sweden	© Maurice de Graaf

The Eckermannite minerals are rare minerals found in some alkaline igneous rocks, as well as some sodium rich contact metasomatic rocks. The eckermannite type locality, Norra Kärr in Sweden is the most prominent locality.

Eckermannite
NaNa₂ (Mg₄ Al) Si₈ O₂₂(OH)₂

Eckermannite is listed from 23 localities in Mindat

Ferroeckermannite
NaNa₂ (Fe²⁺₄ Al) Si₈ O₂₂(OH)₂

Ferroeckermannite is listed from 8 localities in Mindat


Arfvedsonite Root name group

Arfvedsonite, Mt Malosa, Zomba District, Malawi 30cm wide	© A. Rečnik

The arfvedsonite minerals belong to the sodium-amphibole sub-group and they form a solid solution series. They are common in alkali-rich igneous rocks ranging from carbonatite, nepheline-syenites towards alkali-granites. Alkaline massifs often show a gradual development of different alkaline rocks during their active period, and they often contain a large number of different amphibole species. There is not always a one to one correlation between the host rock and its pegmatites with regards to the amphibole specie(s) present. The arfvedsonite bearing Hurricane Mt pegmatites hosted in a riebeckite-granite is a good example.

Magnesioarfvedsonite is the most common arfvedsonite mineral, being abundant in silica under- saturated rocks such as carbonatites and nepheline-syenites. The largest crystals may reach sizes up to 60cm. Arfvedsonite is more typical for alkaline granites and syentites and their pegmatites. The best specimens are found in vugs in these pegmatites, with the recent finds from Malawi as a prime example. It appears that the localities producing the best arfvedsonite-group mineral specimens have a high Fe/Mg ratio, thus being arfvedsonites.

The locality producing the best specimens has historically been Mount St. Hilaire, but as collectors does not have access here today, Mt Melosa in Malawi produces the best specimens today.

There is a continuous series between the arfvedsonite minerals and the corresponding riebeckite-series minerals. There is often an hydrothermal alteration from arfvedsonite to riebeckite in the late stages of pegmatite formation. There is also a continuous series between arfvedsonite and calcium amphiboles such as the hastingsite-series minerals, often also with more exotic intermediate sodium-calcium amphiboles present.

Arfvedsonite
[Na][Na₂][Fe²⁺₄Fe³⁺]Si₈O₂₂[(OH)₂]

Listed from 267 localities in Mindat (Oct 2012)

Fluoro-magnesio-arfvedsonite
[Na][Na₂][Mg₄Fe³⁺]Si₈O₂₂[F₂]

Listed from 8 localities in Mindat (Oct 2012)

Fluoro-potassic-magnesio-arfvedsonite
[K][Na₂][Mg₄Fe³⁺]Si₈O₂₂[F₂]

Listed from 3 localities in Mindat (Oct 2012)

Magnesio-arfvedsonite
[Na][Na₂][Mg₄Fe³⁺]Si₈O₂₂[(OH)₂]

Listed from 61 localities in Mindat (Oct 2012)

Potassicarfvedsonite
[K][Na₂][Fe²⁺₄Fe³⁺]Si₈O₂₂[(OH)₂]

Listed from 7 localities in Mindat (Oct 2012)


Nybøite Root name group

Amphibole containing Ferrinybøite, Vishnevye, Urals Region, Russia 7cm specimen	© Pavel M. Kartashov

The nybøite minerals can be found in some alkaline rocks ( nepheline syenites and others) and as a transition mineral between glaucophane and calcic amphiboles in some eclogites. Normally, the igneous occurrences will be Fe²⁺ and Fe³⁺ enriched, whereas in the metamorphic rocks Mg and Al will be dominant.

An extensive search in petrological literature will identify nybøite minerals from more localities than the handful listed in Mindat, but the nybøites are nevertheless rare minerals. They are never the dominant amphibole at any locality, and each specimen named nybøite should be accompanied by an analysis.

Ferro-ferrinybøite
NaNa₂(Fe²⁺₃Fe³⁺₂)(AlSi₇O₂₂)(OH)₂][/b]

Listed from 4 localities in Mindat (Oct 2012), Three of these localities are in the Khibiny massif, where ferro-ferrinybøite is one of 25 amphiboles in the alkaline rocks there. The fourth locality is the Abdung Zr-Nb deposit in North Korea, which is also associated with alkaline intrusive rocks.

Ferrinybøite
NaNa₂(Fe²⁺₃Fe³⁺₂)(AlSi₇O₂₂)(OH)₂]

Listed from 2 localities in Mindat (Oct 2012), both of them in alkaline massifs.

Ferronybøite
NaNa₂(Fe²⁺₃Al₂)(AlSi₇O₂₂)(OH)₂]

Listed from 4 localities in Mindat (Oct 2012). This is a mineral that has established as a hypothetical mineral by IMA, then later found in nature, but never formally described, so it is also a Named amphibole. It occurs both in alkaline rocks and in high grade metamorphic rocks, such as in the jadeite-almandine-quartz-phengite fels in the Dora-Maira Massif in the Italian alps.

Fluornybøite
NaNa₂(Mg₃Al₂)(AlSi₇O₂₂)F₂]

Listed from 1 locality in Mindat (Oct 2012). It occurs with nybøite and other exotic amphiboles as a retrograde mineral in a kyanite bearing eclogite in Jianchang, China. It should be noted that pargasite is the dominant amphibole in the assemblage.

Nybøite
NaNa₂(Mg₃Al₂)(AlSi₇O₂₂)(OH)₂]

Listed from 6 localities in Mindat (Oct 2012). It occurs mainly as a retrograde mineral in eclogite facies rocks, often as rims or zones on other amphiboles.

Leakeite Root name group

Fluoro-ferroferrileakeite, Khaldzan Buragtag massif, Altai Mts, Mongolia, 50cm hammer	© Pavel M. Kartashov

The leakeite minerals are all very rare minerals found at handful localities worldwide. Except for the large crystalline masses found at the Khaldzan Buragtag massif, they are only found at mm sized or smaller grains and crystals.

Ferroferrileakeite
NaNa₂(Fe²⁺₂Fe³⁺₂Li)(Si₈O₂₂)(OH)₂]

Hypothetical species.

Fluoro-ferroferrileakeite
NaNa₂(Fe²⁺₂Fe³⁺₂Li)(Si₈O₂₂)F₂]

Listed from 2 localities in Mindat. The type locality is the Canada Pinabete pluton, Questa, New Mexico, U.S.A.; where it occurs in association with quartz, alkali feldspar, acmite, ilmenite, and zircon as up to 1 mm long, anhedral bluish black crystals, but the large crystalline masses from the Khaldzan Buragtag massif are truly spectacular for a rare mineral like fluoro-ferroferrileakite.

Fluoro-ferrileakeite
NaNa₂(Mg₂Fe³⁺₂Li)(Si₈O₂₂)F₂]

Listed from 1 locality in Mindat. It occurs as light greenish-blue, isolated prismatic crystals 0.10-2 mm long in a syenitic matrix, in the Norra Kärr, Sweden alkaline intrusion.

Ferrileakeite
NaNa₂(Mg₂Fe³⁺₂Li)(Si₈O₂₂)(OH)₂]

Listed from 2 localities in Mindat, The type locality is the Kajlidongri manganese mine, where it is found in manganiferous metasediments together with several other exotic amphiboles.

Leakeite
NaNa₂(Mg₂Al₂Li)(Si₈O₂₂)(OH)₂]

Hypothetical species, redefined in the 2012 amphibole nomenclature revision (Oct 2012)

Potassic-ferrileakeite
KNa₂(Mg₂Fe³⁺₂Li)(Si₈O₂₂)(OH)₂]

Listed from 1 locality in Mindat (Oct 2012).It is found as prismatic crystals in veinlets composed mainly of quartz, alkali-feldspars, and serandite.in a manganese ore deposit at the Tanohata mine, Iwate Prefecture, Japan. The mineral is considered to be formed under the later stage of hydrothermal activities of contact metasomatism.


Kornite
KNa₂(Mg₂Mn³⁺₂Li)(Si₈O₂₂)(OH)₂]

According to the 2012 nomenclature, this mineral will be renamed Potassic-Manganileakite. It is listed from two localities in Mindat (Oct 2012), both of them associated with manganese ore.


Ferri-ottoliniite
[ ]NaLi(Mg₃Fe³⁺₂)(Si₈O₂₂)(OH)₂]

This mineral is abolished in the 2012 nomenclature. As the type material had Li>Na in the B position, the material is now probably considered to be Ferri-clinoholmquistite

Ferriwhittakerite
NaNa_1+xLi_1-x(Mg₂Fe³⁺₂Li)(Si₈O₂₂)(OH)₂

This mineral is abolished in the 2012 nomenclature. As the type material had Na>Li in the B position, the material is now probably considered to be Ferrileakeite.

Subgroup V: Lithium Amphiboles


Pedrizite root-name group

Pedrizite minerals are known from only two locations worldwide, where they are found as small inclusions in other minerals or as sub-mm sized crystalline aggregates. It is highly unlikely than more than a handful museums or collectors will ever own a verified pedrizite-root name group mineral. There are no photos of any pedrizite mineral in Mindat (as pr. Feb 2012). A photo of "Fluoro-sodicpedrizite" is uploaded to Mindat, but the pictured specimen is not verified and the pictured amphibole may well be holmquistite.

Fluoro-sodicpedrizite?- FOV 3mm	©

These minerals are nevertheless of great scientific interest as these and Li amphiboles in the previous subgroup V found at the same locations have a composition that straddles subgroup I and the sodic amphibole subgroups, and they were one of the reasons for IMA to look into the classification scheme of the entire amphibole group. Pedrizite "proper" has been redefined in the 2012 nomenclature as it is now defined with Na in the A position and (Mg₂,Al₂Li) in the C position. With the introduction of Na in the A position in the root-name formula, the pre-fix "sodic" has become redundant for these minerals.

Ferropedrizite
NaLi₂(Fe²⁺₂Al₂)Si₈O₂₂(OH)₂

Hypothetical end-member, redefined in the 2012 nomenclature.

Fluoro-ferropedrizite,
NaLi₂(Li^Fe2+₂Al₂)Si₈O₂₂F₂

Listed at only one location in Mindat, The Tastyg spodumene deposit, Tuva, Siberia, Russia, where it occurs at the inner contact with lithium pegmatite around oligoclase andesite.

Fluoropedrizite,
NaLi₂(LiMg₂Al₂)Si₈O₂₂F₂

Listed at only one location in Mindat, The Tastyg spodumene deposit, Tuva, Siberia, Russia, where it occurs at the inner contact with lithium pegmatite around oligoclase andesite. This mineral is currently the the only Li amphibole found in nature with Al>Fe³⁺ and Mg>Fe²⁺.

Pedrizite
NaLi₂(Mg₂Al₂Li)Si₈O₂₂(OH)₂

Hypothetical end member

Ferri-ferropedrizite
NaLi₂(Fe²⁺₂Fe³⁺₂Li)Si₈O₂₂(OH)₂

Found only as sub-mm crystalline aggregates in the episyenite ( hydrothermally metamorphosed granites) at Arroyo de la Yedra in the Eastern Pedriza Massif in Spain.

Ferripedrizite
NaLi₂(LiMg₂Fe³⁺₂)Si₈O₂₂(OH)₂

Found only as sub-mm crystalline aggregates in the episyenite ( hydrothermally metamorphosed granites) at Arroyo de la Yedra in the Eastern Pedriza Massif in Spain.

Sodicpedrizite
NaLi₂(LiMg₂Fe³⁺Al)Si₈O₂₂(OH)₂
This name is abolished in the 2012 nomenclature


Holmquistite-clinoholmquistite root name group

Holmquistite, 19mm crystal, Spodumene prospect, Carinthia, Austria	© AC

Holmquistite and clinoholmquistite are in reality two different groups of minerals, and one of them should be renamed in order to follow the principles of the 2012 amphibole nomenclature. The holmquistite-root-name group has a orthorhombic symmetry, and the clinoholmquistite-root-name group a monoclinic symmetri. Since all these minerals are very rare, and have the same root-name it has been more convenient to group them together.

Clinoferroholmquistite
☐Li₂(Fe²⁺₃Al₂)Si₈O₂₂(OH)₂

hypothetical end member

Ferri-clinoferroholmquistite
☐Li₂(Fe²⁺₃Fe³⁺₂)Si₈O₂₂(OH)₂

Described from the metamorphic episyenites in the Pedriza Massif, Sierra de Guadarrama and approved by IMA.

Ferri-clinoholmquistite
☐Li₂((Mg₎₃Fe³⁺₂)Si₈O₂₂(OH)₂

This mineral is described from the metamorphic episyenites in the Pedriza Massif, Sierra de Guadarrama, and are listed in mindat from this locality. The original decription does however show Fe²⁺>Mg, and the mineral described there are therefore not a ferri-clinoholmquistite and this name has consequently quietly disappeared from the IMA list of minerals published at Rruff.info. See also Mindat discussion. In the 2012 nomenclature, it is expected that this mineral is redefined as shown in the formula and that the described material from Pedriza will be considered as ferri-clinoferroholmquistite.

Ferroholmquistite
☐Li₂(Fe²⁺₃Al₂)Si₈O₂₂(OH)₂

Ferroholmquistite is described from the contact zone between the Greenbushes lithium pegmatite in Western Australia and its surrounding amphibolite host rock. Ferroholmquistite occurs as elongated black to bluish-violet prismatic crystals, whose size is typically in the range 0.2–0.5 mm.

Holmquistite
☐Li₂(Mg₃Al₂)Si₈O₂₂(OH)₂

Holmquistite is described from 31 localities in Mindat (as pr. Feb 2012) and is found exclusively in amphibole bearing rocks in contact with lithium pegmatites. Holmquistite is believed formed by metasomatic exchange of elements between the Li pegmatites and the surrounding rocks. Holmquistite are almost exclusively found in the metasomatic altered host rocks for lithium pegmatites.

Sodic-ferri-clinoferroholmquistite
Na_0.5Li₂(Fe²⁺₃Fe³⁺₂Si₈O₂₂(OH)₂

This is an interesting one, See also Mindat discussion.


Subgroup VI: Sodium Mg-Fe-Mn Amphibole Subgroup

No Minerals in this subgroup has yet been approved (sept 2012)

Subgroup VII: Lithium Mg-Fe-Mn Amphibole Subgroup

No Minerals in this subgroup has yet been approved (sept 2012)

Subgroup VIII: Lithium-Calcium Amphibole Subgroup

No Minerals in this subgroup has yet been approved (sept 2012)


^wO dominant amphibole group

Oxo-Sodium Subgroup

This division is not a part of the official amphibole nomenclature, but is introduced in this article to highlight the relationship between the O dominant sodium amphiboles and their (OH) dominant equivalents, illustrated by the single Fe²⁺(OH)₂ <-> Ti⁴⁺O₂ substitution between ferro-ferriobertiite and arfvedsonite.

Obertiite Root name group

Ferriobertiite, Bellerberg vulcano, Eifel, Germany, FOV 0,8mm	© Elmar Lackner 2009

The obertiite minerals are very rare minerals found only in the Eifel area of Germany, and Coyote Peak in California. Both places it is found in xenoliths in intrusive rocks, thus indicating that these minerals are formed in unusula chemical environments at high temperature/low pressure conditions.

Obertiitie
NaNa₂(Mg₃AlTi)Si₈O₂₂O₂

I have introduced composition as the standardized root-name composition in the group. There is no indication in the 2012 nomenclature that it will become an official hypothetical mineral, and it is unlikely to ever be found in nature.

Ferriobertiitie
NaNa₂(Mg₃Fe³⁺Ti)Si₈O₂₂O₂

Ferriobertiitie has been identified from 6 localities in the Eifel volcanic area, where it occurs as small (sub mm) pinkish crystals with sanidine, often tridymite, and sometimes with titanite and pyroxene in xenoliths.

Ferro-obertiite
NaNa₂(Fe²⁺₃Fe³⁺Ti)Si₈O₂₂O₂

This mineral will probably be renamed ferro-ferriobertiite in the 2012 nomenclature. It is known from one locality, the Coyote Peak in California. It occurs as small (up to 1,25mm) crystals with feldspar and aegirine associated with inclusions of lithic-wacke sandstone in an alkali-rich ultramafic diatreme.

Mangani-dellaventuraite
NaNa₂(MgMn³⁺₂TiLi)(Si₈O₂₂)O₂]

The mineral previously named dellaventuraite is in renamed Mangani-dellaventuraite in the 2012 amphibole nomenclature. It is not a change that will impact the average collector, as the mineral is only found at one location, the Kajlidongri Manganese Mine in India. Mangani-dellaventuraite is found as small, reddish grains (up to 1,5mm) associated with leakeite, kornite, albite, braunite, and bixbyite in mn-rich metasedimentary rocks.

Mangano-mangani-ungarettiite
NaNa₂(Mn²⁺₂Mn³⁺₃)(Si₈O₂₂)O₂]


The mineral previously named ungarettiite is in renamed Mangano-Manganiungarettiite in the 2012 nomenclature. It is known from 2 localities in New South Wales in Australia, and the Caspar quarry in the Eifel area of Germany.

Oxo-Calcium Subgroup

This division is not a part of the official amphibole nomenclature, but is introduced in this article to highlight the relationship between the O dominant calcium amphiboles and their (OH) dominant equivalents. New oxo-dominant species equivalents of pargasite,hastingsite, tschermakite etc. can be expected to be identified in the future, as both the substitutions introducing O to the amphibole composition ( Fe²⁺(OH)₂ <-> Ti⁴⁺O₂ and Fe²⁺(OH) <-> Fe³⁺O) are common in calcium amphiboles in volcanic rocks (basaltic hornblendes).


Kaersutite root name group

Kaersutitic amphibole, 3cm crystal, Seletice, Bohemia, Czech Republic	© M. Filippi and P. Magdík

The kaersutite minerals are a mineral group typical for the upper mantle. It is common, even a major constituent of alkali-magmas under high pressures between 25-35 kbar. On surface it can be found as sub mm grains in alkaline volcanic rocks, such as basanites and mugearites, or in alkaline plutonic rocks. Under certain circumstances, titanian amphiboles can also be formed at lower pressures, and it seems as the presence of F- may increase the stability field of kaersutitic amphiboles even at close to atmospheric pressure.

Sometimes, the magma can fractionate and allow larger crystals to form, such as the large, well developed crystals from some of the Czech locations. Kaersutite series minerals may also be fomed in volcanic dikes. This is the case for the type locality Qaersut and also some of the other localities listed in this article.

The Kaersutite minerals are difficult to deal with, even for an amphibole group series. The chemistry, the kaersutite minerals differs from most other amphibole minerals in that one of the space groups in the C position occupied by Titanium, a 4+ cation. Kaersutite and ferrokaersutite are the only minerals (except obertiite) in the amphibole group with a 4+ cation in the C position as a part of the chemical formula.

For most of the locations where kaersutite is known, the Ti content varies randomly between 0,3 and 0,7 apfu, or in other words, the actual mineral varies randomly between pargasite and kaersutite. There are no way to tell the difference without a quantitative chemical analysis for the individual crystal, Even within the same location, the same rock, or even within the same crystal, this variation takes place.

Ferrikaersutite
NaCa₂(Mg₃Fe³⁺Ti)(Al₂Si₆O₂₂)O₂

Ferrikaersutite has been described from the volcanic rocks in the Gregory Rift in Tanzania

Ferro-kaersutite
NaCa₂(Fe₃AlTi)(Si₆Al₂)O₂₂)O₂

This mineral is found in volcanic rocks and 8 localities are listed in the Mindat database.(sept 2011)

Kaersutite
NaCa₂(Mg₃AlTi)(Si₆Al₂)O₂₂)O₂

This mineral is found in volcanic rocks and 138 localities are listed in the Mindat database. (sept 2011). Prior to 1978, the borderline between pargasite and kaersutite was not unambiguous. For kaersutite references older than 1978, analytical data should be checked to verify Ti>0,5apfu. The 2012 nomenclature has strengthened the requirements for O>(OH), which may require further verification of analytical data to clarify whether a given amphibole qualifies as a kaersutite mineral or not.


Olav Revheim October 2012

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Edited 13 time(s). Last edit at 10/08/2012 06:25PM by Olav Revheim.

Olav,
Your work is progressing nicely. I look forward to watching it grow.

Rock Currier
Crystals not pistols.