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Posted by Olav Revheim
Olav Revheim November 30, 2010 09:44PM
Click here to view Best Minerals H , and here for Best Minerals A to Z and here for Fast Navigation for finished Best Minerals articles.
Can you help make this a better article? What good localities have we missed? Can you supply pictures of better specimens than those we show here? Can you give us more and better information about the specimens from these localities? Can you supply better geological or historical information on these localities?
Magnesiohornblende and Ferrohornblende are minerals in the Amphibole group, see Amphibole Group main article for an overview of the group. In addition to these IMA approved minerals, the article also includes hornblende and Fluoromagnesiohornblende.
Fluormagnesiohornblende ( Not IMA Approved)☐2>
Hornblende (NOT a valid mineral)(Ca,Na,K)2–3(Mg,Fe,Al)5(Al,Si)8O22(OH,F)2 monoclinic
The name "Hornblende" as a term is widely used for many species of amphibole minerals, and used to be a valid mineral name with the chemical formula (Ca,Na)2–3(Mg,Fe,Al)5(Al,Si)8O22(OH,F)2. This general formula covers almost all minerals in the sodic-calcic-clino-amphibole and calcic-clino-amphibole subgroups. "Hornblende" is still used as a handy name to describe dark amphiboles within these subgroups. With this discredited, wider definition of the "mineral", "hornblende" was considered a common mineral in many different geological settings of igneous and metamorphic origin.
Today, the minerals magnesio- and ferro-hornblende are specified with a lot narrower chemical boundaries. The hornblende minerals are closely related to the tremolite-actinolite series ( contains less Al), tschermakite-series (contains less Si) and the edenite-series (contains Na or K in the A position). There are continuous series between all of these minerals ( and more), and the composition is often intermediate between several different minerals as illustrated by the classical "hornblende" from Arendal, Norway. Magnesio- and ferro-hornblende have similar physical appearance to several of the other amphibol group minerals as well, making identification without chemical and structural analysis impossible.
Even if it is many years since the name "hornblende" was redefined, there are still some confusion about how and when an amphibole species can be assigned a name in the hornblende-series. For many of the amphibole entries in Mindat the name "hornblende" is probably (obviously) used as a field term for any dark amphibole, and the naming in these cases provides little sense ( Yes, I am guilty of doing it aswell). Even IMA approves the use of "hornblende" as a general term describing an unspecified dark amphibole group mineral in the calcio-clino-amphibole subgroup, but without placing "hornblende" in the formal amphibole hierarchy. It also seems that for some locations the old name "hornblende" is substituted with ferrohornblende. This practice is plain wrong and definitely misleading. I suspect that some of the entries in this article may fall in this category.
Many museum species or specimens from classic localities are labelled "hornblende", and quite often this naming is backed by a chemical analysis supporting the discredited name. Unfortunately, a chemical analysis alone does not help much, as the individual amphibles found in nature will normally be of an intermediate composition, and a given chemistry may be attributed to a number of species based on how the different elements are organized in the amphibole structure. I have included quite a few of these specimens in the article, highlighting in each case that these "hornblende" specimens may in fact be a different species. Where I have found a chemical analysis published on the net, I have included this in the description.
The number of confirmed ferrohornblende and magnesiohornblende entered into the Mindat database is not impressive. I suspect this is partly because determining the the exact species is a quite expensive and tediuos task, and partly because the hornblende series minerals is not that common in isolated well formed crystals. Based on the few entries, it seems that the ferro- and magnesiohornblende most frequently occur as phenocrysts in lava flows or as small crystals in cavities in volcanic rocks or contact zones. Some magnificent photographs of ferrohornblende from the Italian lava flows are included in the article. Ferrohornblende is also confirmed from the metamorphic iron ores of Northern Sweden, where large, well-formed crystals often covered with stilbite or calcite. The large crystals of magnesiohormblende from Akland, Norway have formed in a metagabbro with partial hydrothermal alteration.
Normally these amphibles are not very popular amongst collectors as it is hard to see how a specimen can be very attractive. Also, the cost of accurately identifying a specimen will exceed the value of the specimen itself many times. It appears that Ferro-hornblende and magnesio-hornblende is identified from locations rich in variuous minerals and that identifying the mineral species is worthwhile only to avoid listing "unidentified amphibole group" mineral on the mineral lists. Common for most of these locations is that more than one amphibole group mineral is present, so that identification by simple means is still very difficult.
Ontario, Haliburton Co., Monmouth Township ,Tory Hill
There are several amphibole locations categorized under the Tory Hill location. The best known of these are the Bear Lake Diggings described below.
The amphibole crystals occurs in the contact zone between the host rock and calcite veins. Several amphibole-species have been described from this area, and the name "hornblende" is used as a field name for any un-identified amphibole.
Ontario, Haliburton Co., Monmouth Township ,Tory Hill, Bear Lake diggings (Gibson Road Western occurrence)
The Bear Lake Diggings are located 8,4 km west of Tory Hill. The mineralization is found in calcite veins up to 1,5m wide and 120 m long. The location is most renowned for fluoraptite crystals up to 50cm long, but nice amphibole crystals up to minimum 20cm have also been found.
Those analyzed has proven to be edenite-, kataphorite- and richterite series amphiboles that are impossible to distinguish without proper analytical work. The term hornblende has been and are used as a convenient name to describe any brown or black amphibole in the calcic- or sodic-calcic subgroup.
To my knowledge, neither magnesiohornblende nor ferrohornblende has been confirmed from this location.
Czech Republic ,
Bohemia (Böhmen; Boehmen), Ústí Region, Teplice (Teplitz)
The pictured crystals are in the collection of the Academy of Natural Sciences of Philadelphia. These crystals was probably collected a long time ago, and where found as crystals embedded in basalt, as described in the locality description for the modern Dolanky basalt quarry near Teplice: "Basalt quarry near small village 10km east by south from Teplice. Top, half mining floor is created on to west by south area pillars of right basalt. This basalt is without cavities and verge into dark stale basalt with large crystals of Amphibole"
These hornblende crystals are an example of amphiboles from old collections that are labeled named hornblende based on the valid nomenclature at the time. Whether or not they would be called hornblende today is quite uncertain.
Länsi-Suomen Lääni , Turku-Pori , Pargas (Parainen), Ersby
Specimen is from the collection of the British Museum of Natural History #59416 (1975). The locality at Ersby is an old limestone quarry that was in opration from 1740 - 1800. The total limestone outtake is estimated to 400,000 tonnes. It is not unlikely that this specimen was found when the quarry was in operation.
This is another example of an old specimen labelled hornblende in accordance with the nomenclature of the time. Pargasite was described from Pargas, Finland in 1814, and this specimen may well be a pargasite predating the first description of pargasite as a separate species.
Lapin (Lapland), Kolari Lääni, ,Hannukainen mine
The Hannukainen mine lies in the western margin of Central Lapland greenstone belt (CLGB). It is a deposit that was mined in 1978–1992. The deposit is a iron oxide-copper-gold deposit including five main ore bodies all variably enriched in Au, Ca, Cu, K, Mg, Na, Fe, and S. The ore is hosted by massive to banded diopside-hornblende- and magnetite rocks, in the contact zone between a 1.86 Ga monzonitic intrusion and the supracrustal CLGB rocks. The supracrustal rocks are metamorphosed to lower amphibolite facies. Sulphides and gold postdate diopside, hornblende and magnetite, and the age dating at site suggest epigenetic Au-Cu mineralisation postdating the monzonite by ca. 40 Ma. Native gold, all or most of it, closely associated with chalcopyrite, magnetite and gangue: inclusions in pyrite with chalcopyrite, in cracks is magnetite and pyrite, inclusions in chalcopyrite.
Amphibole minerals can be in three different mineral assemblages:
1) Amphibolite: hornblende-plagioclase ± biotite, titanite, magnetite, epidote.
2) Exoskarn: magnetite-diopside-amphibole-plagioclase ± scapolite, sulphides, epidote, garnet, gold.
3)Endoskarn: 20-200 m wide zone, albite to oligoclase-quartz ± hornblende, diopside, scapolite, epidote, biotite, magnetite, pyrite, chalcopyrite
I think it will be fair to assume that more than one amphibole mineral can be present at this location. I have not found any details on maximum size, quality or composition of the "hornblende" from Hannukainen.
Auvergne, Haute-Loire , Le Puy-en-Velay, Espaly-Saint-Marcel , Riou Pezzouliou
This and the next location does not produce outstanding display specimens, and the quality of the specimens from a purely estethic perspective can be discussed. These locations are nevertheless truly remarkable in that the "hornblende" is found in isolated, well formed crystals in alluvial sediments. Amphiboles are prone to both chemical and mechanical degradation and is far rarer in sediments than it's abundance in igneous and metamorphic rocks should indicate.
The Riou Pezzeouliou is a small creek, and hornblende is found in the sediments together with numerous other minerals. The term hornblende is used here, I assume, as a field term for dark amphibole of uncertain composition.
Centre, Loiret, Gien, Loire River alluvials
At this location, hornblende is found in concentrations of "heavy sands" with numerous other minerals. The pockets of heavy sands is normally below water level.
I have not found any references besides the information provided by the uploader to confirm this amphibole as Ferrohornblende.
Hesse , Vogelsberg , Ranstadt, Steinknorre
The pictured hornblende crystals was found in outcrops of basalt slags and tuffs on the north slope of Steinknorre hill, 1.5 km south of Ranstadt in a profilic occurence during road cut of B 275 around 1970.This is now (2008) mostly overgrown.
"Hornblende" has been known from the Vogelsberg area for a long time and Thomas Thomsen publishes a chemical analysis as early as 1836 in his "Outlines of mineralogy, geology, and mineral analysis". This analysis ( Silica: 42.24, magnesia: 13.74, Lime: 12,24, Alumina: 13,92, Protoxide of iron: 16,26 and Protoxide of Manganese o,33) indicates that this "hornblende" is of an intermediate composition and only a thorough structural analysis can determin the mineral species.
Latium , Viterbo Province , Vico Lake, Vetralla, Tre Croci
The Vico vulcano is relatively recent (420,000-100,000 yrs old) and is a stratovulcano with a central caldera, hosting the Vico Lake, and a few small circum-caldera centers. The volcano erupted silica-oversaturated to undersaturated potassic and ultrapotassic magmas.
Like other Roman volcanoes, the Vico pyroclastic rocks contain xenoliths of various origin, including bedrock fragments, intrusive equivalents of lavas, and cumulate rocks. These xenoliths often contain exotic minerals, such as Zr-Ti-Th-U-REE rich phases (e.g. britholite, baddelyite, and pyrochlore), which have been interpreted to be the result of deposition
from late-magmatic fluids rich in incompatible elements (e.g. Della Ventura et al. 1999). The pictured ”hornblende” crystal is probably found in this environment.
Even if magnesiohastingsite is described form some of the trachytes (Pecerillo), it is quite likely that several different amphiboles are present in the lavas, pyroclastics and the termometamorphic xenoliths, due to the varying chemistry of the different lavas and the xenoliths. One should be very careful when attributing a mineral name to an amphibole from here.
Latium, Viterbo Province, Onano, Montenero quarry
Magnesiohornblende at this location occurs in pyroclastic formations, in a similar fashion as the previous location. Magnesiohornblende occurs as mm-sized well developed crystals. Also magnesiohastingsite is described from the location, but this mineral has a different appearance.
The magnesiohornblende is determined by standard two-point SEM/EDX. (Marco E. Ciriotti(2011): Associazione Micro-mineralogica Italiana forum, see also http://www.mindat.org/mesg-106-237297.html
Tuscany, Grosseto Province, Pitigliano , Case Collina (Toscopomici quarry )
This location is a part of the Latera Volcanic complex and the mineralization is found in vugs in pumice deposits. The amphibole minerals have not been identified, and it is not unlikely that more than one amphibole mineral is present.
Campania, Naples Province., Somma-Vesuvius Complex, Monte Somma
The Somma-Vesuvius is a composite central volcano composed of an ancient stratovolcano, Mount Somma, and more recently by a cone, the Vesuvius. The age of the oldest products in outcrop is about 25,000 years.The latest round of activity seems to have ended with the eruption of March 1944. This eruption was the beginning of a resting phase characterized by modest signs of seismic activity and fumarole (Arno et al., 1987).
More than 230 species has been found in this area, and is one of the most interesting places in Europe. There are in principle four different mineral forming environments, each with a different mineral assemblage;
I. Minerals that are found in the ejected limestone blocks of Monte Somma.2
II. Pneumatolytic minerals formed in cavities of leucotephrites and conglomeratic blocks ejected by Monte Somma and Vesuvius, or coating the walls of ancient lavas.
III. Fumarolic products.
IV. Minerals that occur as rock constituents of Vesuvius and Monte Somma.
Amphibole minerals can be found in all of these mineral forming environments, but I have not been able to pinpoint a specific environment for the ferrohornblende.
Campania, Naples Province., Somma-Vesuvius Complex, Monte Somma, San Vito, Ercolano, San Vito quarry,
This occurance is an abandoned pumice quarry that has been very rich in minerals. The occurance of feroohornblende in this quarry is confirmed, and it occurs in small ( mm-sized) well formed crystals.
Honshu Island , Chubu Region, Nagano Prefecture, Suwa-gun, Fujimi
These crystals seems to have formed as phenocrysts in volcanic rocks.
Meknès-Tafilalet Region, Khénifra Province , High Atlas Mts, Tamazeght complex , Bou-Agrao Mt
The Eocene Tamazeght complex, High Atlas Mountains, Morocco is a multiphase alkaline to peralkaline intrusive complex. A large variety of rock types (including pyroxenites, glimmerites, gabbroic to monzonitic rocks, feldspathoidal syenites, carbonatites and various dyke rocks) documents a progression from ultramafic to felsic magmatism.
According to Marks M. A. W. et al. (2008): listed at a reference for this location, the amphiboles found here are not hornblende:
"Following the nomenclature scheme of Leake et al. (1997), all analyses are calcic amphiboles of hastingsitic (AlVI ≤ Fe3+) and kaersutitic (Ti ≥ 0·5 p.f.u.) composition."
Aust-Agder, Risør, Akland
Several minerals at relatively good quality was found at Akland in 2002/2003 in a relatively small area during road construction work at a highway exit. The geological environment are high amphibolite facies/granulite facies metasediments and metagabbros. The magnesiohornblende was found in a large vug system in a gabbro pegmatite with diopside and actinolite and partly covered with small albite crystals.
It seem like that the more than 10cm long magnesiohornblende crystals are pseudomorphs after diopside, as one could follow the different stages of transformation from diopside via magnesiohornblende to byssolite/clays.
I don't know the total amount of specimens that where retrieved from these vugs, but the total volume was sufficient to meet the demand of the domestic market, and specimens should still be available.
Aust-Agder , Arendal
From 1574 to 1975, some 350-400 mines, quarries and prospects was opened to mine magnetite from skarn rocks. The iron production from the operating mines provided a significant input to the Danish-Norwegian economy through several hundred years. "Hornblende" was one of the main constituents of the skarn rocks together with andradite, epidote, scapolite, plagioclase feldspar and others. Most museums acquiring minerals from 1850 onwards will have mineral specimens from Arendal. Many of the specimens collected are of quite good quality with large (>10cm) well formed crystals formed on the border zone between the skarn and the calcite.
Bjørlykke (1959) has published a chemical analysis of this material, and this analysis seems to indicate that this material may be either actinolite/hornblende series or edenite series based on how Fe, Mg, Al and K/Na are distributed in the amphibole structure. It may also be that an eventual closer investigation of this material may reveal multiple amphibole species with very similar appearance. As most of the specimens secured are in old museum collections and without any significant value, it is quite unlikely that such investigation will take place..
The locations now are mostly inaccessible. All mine shafts are secured and the dumps are either developed as industrial or housing environements, used as gravel material or heavily overgrown, with a very few exceptions.
Buskerud, Modum, Snarum , Oksøyekollen (Oksøykollen; Oxøiekollen)
Telemark , Kragerø , Stussdalen (Studsdalen)
Stussdalen is one of the classical "hornblende" localities in Kragerø district, and is used in this article as an example of the a location from the district. Any "hornblende" specimen older then the 1960-ties is probably from another location in the vicinity of this. Stussdalen is still producing specimens with crystals up to 30 cm long. The crystals from Stussdalen are rarely terminated, and if so the terminations are split up into hairlike asbestos.
The location is a small clay(?) filled fracture no more than 5-10m high within an amphibolite body. The "hornblende" crystals can be found as free floating crystals or growing into the clay from the amphibolite. The "hornblende" crystals are crisscrossing within the fracture and it is tedious work to free undamaged crystals.
It is difficlut to free matrix specimens, so most of the specimens from here are single crystals.
I have not seen any of the "hornblende" specimens accurately identified, but as they are found in various geological enironments, it will not surprise me if there are several amphibole species in the area
Urals Region ,Southern Urals, Chelyabinsk Oblast', Chelyabinsk coal basin, Kopeisk, Coal mine No. 45
This mineral is one of many that are formed in the burning coal dumps burned spoil-heaps of the Chelyabinsk coal basin, Russia. The new minerals have been formed as a result of local thermal reactions between gases coming from the coal fires and sedimentary carbonates and silicates. The fluorine rich minerals has been formed by reaction between these rocks and fluorine gas. The formation of CaF2 and MgF2 has reduced the required temperature for the ractions to take place. MgF2 combined with very dry conditions are responsible for forming fluoromagnesiohornblende from silicate sediments.
Andalusia, Almería, Carboneras
The ferrohornblende(?) is found as phenocrysts in andesine lava.
Andalusia, Seville , Lebrija ,Minera I Quarry
It appears from the reference for "ferrohornblende" from this location ( http://mti-minas-andalucia.blogspot.com/2008/11/mina-minera-i.html) that the amphibole from this location is actinolite.
Canary Islands , Santa Cruz de Tenerife Province , Tenerife, Fuente de Joco
Ferrohornblende(?) are found as phenocrysts in lava flows.
Lappland, Gällivare, Malmberget
Malmberget (ore mountain) iron ore mine, located at Gällivare, 75km from Kiruna, contains some 20 orebodies spread over an underground area of about 5 by 2.5km. Seven are currently being exploited. Mining began in 1892, since when over 350Mt of ore have been won.
Malmberget's ores ( mainly magnetite, but also hematite) are hosted in Precambrian volcanic rocks that have largely been metamorphosed to gneisses. Containing apatite-bearing iron ore, the entire deposit complex has been strongly folded and now consists of a number of ore sheets that may have originally been connected. Most orebodies lie within the 6.5km-long main ore zone.
The mineralizaion of interest for collectors are formed later than the ore bodies in large voids in the rock formed by folding action during the methamorphosis. Only a minority of the voids carry crystallized minerals, predominantly calcite and zeolite, but also ferrohornblende ( Lyckberg 2006). Ferrohornblende may occure as large well formed crystals in these voids, sometimes overgrown with stilbite and calcite.
Scotland, North West Highlands (Inverness-shire), Isle of Skye, Luib, Eas a Bradain
The Ferrohornblende from this location is confirmed with XRD and EPMA, and is one of the few locations where a hornblende-series mineral has been positively ID'ed. In addition to Ferrohornblende, several other amphibole species are recorded from the area. Minerals form the Eas a Bradain location consists of various locations within a rather large area (multiple sq.km.)
The minerals are found in miarolic cavities up to 6 cm in an epigranite, and the material is mostly micromounts.
Massachusetts, Worcester Co., Bolton, Bolton Lime Quarries (Bolton quarry; Whitcomb quarry; Hildreth quarry
The Bolton locality consists of two limestone (marble) quarries about 1/8 mile apart, and a lime kiln and dumps in between the quarries. John Whitcomb (1712-1785) is believed to have been the first to work the deposit sometime in the 1730s. The north and larger quarry was known as the Whitcomb quarry. The south quarry was called the Hildreth Quarry. The Whitcomb quarry was operated until the 1860s and reopened briefly in 1937 for 2-3 years.
The quarries are in a limestone (marble) unit enclosed in gneiss. According to Emerson (1917): "Where gneiss is in contact with limestone in the quarries at Bolton a layer of black porphyritic diorite 3 or 4 feet thick is commonly next to the limestone. Where this diorite or the fine biotite granite in the gneiss touches the limestone the layer next to it is in some places composed of vein quartz, but ordinarily it is a thick sheet of scapolite rock, in one place 16 feet thick. Next comes a light green pyroxene hornblende layer and next a layer of boltonite
The magnesiohornblende (analyzed, SEM-EDS) seems to come from the pyroxene/hornblende layer.
Massachusetts , Franklin Co., Hawley
New York, Jefferson Co., Wilna Township, Natural Bridge
The Jefferson and Lawrence Counties of USA host a large number of great mineral locations in the metasedimentary and metasomatic Precambrian rocks formed in the Grenville orogeny. The area is one of the classic sources of mineral specimens, shown by the following quote:
“No introduction to the minerals of the western Adirondack region in upper New York State need be given to any one interested in mineralogy. Good crystals from its many localities adorn nearly all mineral collections and most of the easily obtainable show specimens were taken long ago. There is still a great deal left, however, which will repay a trip into the region.”
The quote is taken from “The Minerals of St. Lawrence, Jefferson and Lewis Counties, New York.” By W.M.Agar, Princton University, 1921.
I have not been able to positively conclude that the pictured "hornblende" crystals are in deed hornblende-series minerals. They may well be minerals in the tremolite-hornblende series or edenite series using the current nomenclature. These dark amphibole crystals can, like the tremolite (http://www.mindat.org/mesg-86-198178.html) from the same type of occurances be found in relateively large, well formed crystals.
New York , St Lawrence Co., Russell
Fast Navigation for finished Best Minerals articles.
First Draft Completed by Olav Revheim Feb 23rd 2011
Edited 36 time(s). Last edit at 07/15/2015 11:17AM by Olav Revheim.
Rock Currier February 17, 2011 08:43AMOlav,
Let me congratulate you on doing a fine job on the article. You have learned the fine art of arranging and tweaking the images to make them look attractive including the addition of the period to provide a spacing between vertically stacked images and think you are only the third person to learn how to do this. I am glad you made the announcement about finishing the first draft for the article in the general forum, but don't feel bad if no one or only two or three people respond to your request for further information. You will find that in time that the responses will come dribbling in and bit by bit you can improve and add to your article. Make sure that the fast navigation links appear at the bottom of the article as well as the top and put the date when you finished the first draft at the bottom of the article so that when you or someone else in the future wants to add to the article they can use that date to look in the image bank for new images that have been uploaded. Also make sure that you add Hornblend, Ferrohornblende, Magnesiohornblende and Fluormagnesiohornblende to the fast navigation list in the Welcome to Best Minerals forum.. Once again congratulation on an excellent job.
Crystals not pistols.
Tim Jokela Jr June 18, 2013 05:14PMMight want to point out that the "hornblendes" from Ontario are surely the largest and finest in the world. I don't want to quote specific dimensions without doing further research, but crystals far, far larger than 20cm have been found. I saw one in situ that was fence post size; this was the 80's, supposedly it was being collected by a museum. I assume it's in the ROM or CMN. Good but smaller xls are still abundant in the area.
Olav Revheim June 18, 2013 06:39PMThank you Tim.
I agree that they probably are the largest well formed "hornblende" crystals there is. They have been included here, here, here and here but not in the hornblende article.
As you know, there is a difference between the term hornblende used in petrology and the magnesio-hornblende-root-name-group as defined in the CNMNC amphibole nomenclature. The first use is for any calcic, Al-bearing amphibole of non-sufficiently analysed composition , whereas the second is for the strictly defined minerals that hardly anyone bothers to do the necessary work to find out they have. I guess that most of the Ontario "hornblende" is either edenite-richterite group minerals or tremolite-actinolite series?
The problem with this article is that it does not distinguish between the two different ways to use the name hornblende, and it is not consistent with the other amphibole best minerals articles here, and I haven't yet found out how to deal with it. Ideally, I would like to restrict this article to the IMA meaning of the term hornblende as this is a mineral site, but I don't know if that is possible.
I plan on revisiting all of the amphibole articles in the not too distant future and I would appreciate any suggestions.
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Copyright © mindat.org and the Hudson Institute of Mineralogy 1993-2016, except where stated. Mindat.org relies on the contributions of thousands of members and supporters.