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Re: Cordierite

Posted by Olav Revheim  
Re: Cordierite
October 20, 2009 07:07PM
no    
Click here to view Best Minerals C and here for Best Minerals A to Z and here for Fast Navigation of completed 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? After each set of pictures there should be some descriptive text. If none appears it means that we need someone to tell us about the specimens from that locality and something about the geology of the occurrence.



Cordierite
(Mg,Fe)2Al4Si5O18

Cordierite, Søndeled Norway, 8cm specimen© Jan Kihle

Cordierite is a rock forming mineral that can most frequently be found in metamorphic rocks exposed to high pressure and temperature ( high amphibolite, low granulite facies). In addition to the temperature and pressure limitations for its formation, cordierite can not be formed in environments rich in Fe, K and Ca. If these elements are present, feldspars, garnets and mica will be formed rather than cordierite.

Despite these limitations, cordierite is a widespread mineral, and some rocks can contain as much as 20-30% of the mineral. Cordierite is an important mineral for petrologists, using it to determine the geological history of rock sections. In particular the cordierite/anthophyllite rocks of Orijarvi, Finland have a special historical interest, as Eskola (1914) outlined the theory on metamorphic facies based on studies on these rocks.

For those of us more interested in cordierite mineral specimens, it is quite easy to become a bit disappointed. Like many minerals predominantly found in metamorphic rocks, large well formed crystals and crystal clusters are quite rare. They can be found though, most frequently associated with quartz in coarse grained sections of cordierite bearing rocks. Since cordierite is a rock forming mineral, and not often found in nice well developed crystals, I sit with a feeling that many of the best collecting sites are yet to be described. Many of the areas where the geology seems right for cordierite specimens such as East Africa, India and the Andes, none or a very few locations are described. The reason seems to be the relative unattractiveness and low value of cordierite compared to other minerals. In the few locations where cordierite has been described as gems or crystals specimens are often brought to market as specimens found when looking for something else. The locations described in this "best minerals" article are therefore unintentionally and unavoidable biased towards European and North American locations

Cordierite is not stable in the pressure and temperature regimes normally found at or near the earth’s surface. The internal structure of cordierite is such that the water molecule can easily enter its structure and form other minerals. As a result, cordierite crystal will normally be covered by a layer of alteration products. Quite frequently the entire cordierite mass is pseudomorphed, and a wide range of different “mineral names” has been given to these alteration products. They are normally a mixture of different minerals, normally Mg and Al rich sheet silicates in the mica, chlorite and clay subgroups.

The relative ease of chemical alteration of cordierite makes it a rare mineral in igneous rocks. but it does occur in fabulous microcrystals in xenolithes in erupted lavas.

Even without crystal shape and with an alteration layer, cordierite can be of interest. Many places it is found in facet grade quality, and provides clear blue gems, similar looking, but less expensive than sapphire and tanzanite. As cordierite is harder than quartz, it is quite suitable as a gemstone, although it has a very distinct pleochlorism that must be taken into consideration while cutting the stone.

Due to it’s strong pleochlorism it has been claimed that cordierite has been used by the Vikings as a polarizing compass. The theory was first launched in 1967 by the Danish archeologist Torkild Ramskou. The idea is that a polished piece of "sunstone" is turned in the air, the direction to the light source ( read the sun or the moon) can be determined, even in overcast, dark and foggy weather. The theory has been supported by different researchers, latest by a team of Hungarian scientists, (see [news.bbc.co.uk] ). It has been claimed that cordierite or optical calcite ( Iceland spar) has been used for this purpose. ( see Leif Karlsen “Secrets of Viking Navigation" and [www.mindat.org] ). A paper published in Applied Optics concludes that “The use of polarized skylight for navigation under partly cloudfree skies should be treated with caution and skepticism.” (Curt Roslund and Claes Beckman, "Disputing Viking navigation by polarized skylight," Appl. Opt. 33, 4754-4755 (1994). I guess it is a lot easier to postulate a theory than proving it wrong.

Moving back to the mineral cordierite, most museums carries several cordierite samples, but few have really good display specimens. Several US museums will have well crystallized specimens from Richmond, New Hampshire. The Canadian province of Manitoba has also yielded some outstanding specimens. Some of the Norwegian museums have good specimens, amongst them the privately owned Lom Steinsenter.

Well crystallized display size cordierite specimens can reach a retail value of several thousand USD, wheras the gemstone ( often called iolite or water sapphire) is a more affordable alternative to sapphire and tanzanite.

Picking the best minerals and locatons for cordierite has been a rather difficult task. It is a very common mineral, but does not often occur in good crystals. If you go for the largest, sharpest and highly priced crystals, Richmond, New Hampsire, USA seems to be high up there, with possibly a few other locations. Being a quite popular gemstone, it is hard not to include the best gem localities, and the perfect, transparent microcrystals from the Eiffel mountins in Germany simply cannot be ignored, and it is equally difficult to ignore all the exciting pseudomorphs that’s out there. Consequently, the “ best mineral” section will contain "best minerals" selected by four differnet criteria; largest display size crystals, best gems, best microcrystals and best codierite pseudomorphs.
[Olav Revheim 2010]


Cordierite
Bolivia
Potosí Department, Rafael Bustillo Province, Llallagua, Siglo Veinte Mine (Siglo XX Mine; Llallagua Mine; Catavi)

Cordierite, ~7cm wide©

The Sieglo Viente Mine located more than 4000m above seal level in the Bolivian Andes mountains. It was opened in the early 20th century and was at one stage one of the richest tin deposits in the world. The mine is also rich in mineral species with more than hundred differnt minerals described and it is the type locality for 5. The tin deposits are of hydrothermal origin in veins in a quartz porphyry breccia. The rich mineralization is the result of several igneous and hydrothermal events creating several different mineral forming environments. The cordierite originates from recrystallized aluminium-rich marine sediments. ( Hyrsl, J. & A. Petrov (2006) Famous Mineral Localities: Llallagua, Bolivia. Mineralogical Record 37: 117-162. and Michael S.J. Mlynarczyk *, Anthony E. Williams-Jones( 2005) The role of collisional tectonics in the metallogeny of the Central Andean tin belt. Earth and Planetary Science Letters 240 (2005) 656–667)


Cordierite
Brazil
Southeast Region, Minas Gerais, Coroaci, Virgolândia

Cordierite, 1.6cm wide© Rob Lavinsky
Cordierite, etched floater 1.5cm tall© vasco trancoso

The village Virgolândia lies in the middle of the São José da Safira Pegmatite District, Northwest of Governador Valadares. The districts hosts a wide range of gemmy tourmaline and beryl bearing pegmatites, but there is no mention of any cordierite-bearing pegmatites in the litterature I have access to. It is more likely that the cordierite location is related to the amphibolite-facies mica shists and quartzite rocks surrounding the pegmatites, but I have not been able to find any specific information on a cordierite location in this area, and any information on this and/or similar locations will be highly appreciated.

Cordierite
Canada
Ontario, Thunder Bay District, Manitouwadge, Geco mine

The Geco Mine is located near Manitouwadge north of Lake Superior on the US/Canadian border. The mine has been run on a large sulphide ore body of vulcanic origin. 55 mill ton ore was produced in the period 1957-1995, mainly chalkopyrite. (USGS Mineral resources database)

"Many years ago I drove through Manitouwadge after a tip by Charlie Key who told me this copper mine produced good gem quality Cordierite. I located the sample man at the mine and he sold me and later sent me some rather nice pieces of rough gemmy Cordierite, some of which I had cut into small gem stones. They were a little "sleepy" looking. Many years later I was in Elco, Nevada attending an MSHAW training course on mine safety so I could collect underground at Elmwood, Tennessee. That never came to pass, but in that class were an entire range of people who wanted to work in the various gold mines in northern Nevada. Even if you were going to drive a water truck on the surface at a mine site you had to have the course. One of the guys in the class never had much to say. Eventually I got to know him a bit and he had been an underground miner for 20 years but still had to take that dumb class. He got to know me a bit and of my interest in mineral specimens. One day he asked me if I knew a mineral that was white and blue at the same time. I told him that I did not, but did know one that was pale yellow blue. Cordierite. I told him that the best locality for the mineral in North America was the Geco mine. He seemed very surprised and then told me that he had been a miner at the Geco Mine for many years and that they used to get large pieces of the material in the scram. The scram is a bucket device that is pulled back and fourth by a cable to drag and move blasted rocks, in this case to a grizzly. The grizzly he was talking about was a hole covered by thick steel bars that lets fragments below a certain size fall through them into a chute or onto a conveyor belt. I ask him if this was the kind of stuff that would show blue when he put his mine lamp behind the piece and he confirmed that it was. I then ask him how big the pieces got. He told considered for a minute and then pointed to a blue plastic trash can in the corner of the room of about 30 gallon capacity. He told me that he had helped the mine manager build a fireplace in his home from the material. To this day I believe that in one of the modest homes in Manitouwadge is one with a fire place that is worth more in gem grade iolite than the house is worth. I just shook my head and told him that if he had collected a garage full of the stuff that he could have retired on the proceeds. All the material I ever saw from this locality was massive and I never saw or heard of a well formed crystal."
[Rock Currier 2009]

The cordierite was found in a gedrite/cordierite bearing host rock. The gedrite/cordierite gneiss originated from acidic supracrustal (formed at the surface) volcanic tuff originating from the same orogeny creating the sulphide ore. The rock formation Manitouwadge greenstone belt is metamorphosed to high amphibolite facies forming the gedrite/cordierite gneiss. It is quite widespread in the area, and the potential for finding more cordierite should by present. ( Seismic Methods in Mineral Exploration: Paper 56- Seismic Exploration of the Manitouwadge Greenstone Belt, Ontario
Roberts, B., Zaleski, E., Adam, E., Perron, G., Petrie, L., Darch, W.,Salisbury, M.H., Eaton, D., and Milkereit, B.)
'

" Geco mine, Ontario [www.mindat.org] has produced very fine gem material." 2009 Phillipe M. Belley

Cordierite
Canada
Manitoba, Snow Lake, Stall Lake Copper Mine

"Manitoba has some insanely nice/large cordierite crystals." 2009 Phillipe M. Belley
From what I can understand the Stall Lake Copper Mine is the prime source of cordierite from Manitoba.

"The orebody here was a Volcanic rock associated, Stratabound Massive Sulphide Type Deposit. The mines depth went to over 4000 feet. Cordierite crystals up to 0.6 m long and 15 cm in diameter had been seen with Chlorite reaction rims in the Alteration Zone during mining operations. They are from the # 4 Orebody, 3341 Stope Alteration Zone of the now defunct Stall Lake Copper Mine" Bob Southern 2009. He also attached images of nice cordierite crystals from this mine.

"The copper-zinc deposits of Stall Lake Mines Ltd. in the Snow Lake area of Manitoba are interpreted as being of metamorphosed volcanogenic origin. Some of the massive chalcopyrite and sphalerite ores occur in highly elongate, stratiform lenses. Known deposits occur in the uppermost layers of a thick rhyolitic ash formation, now resembling quartz "porphyry," near its contact with overlying basaltic tuffs and flows. Metamorphism to the amphibolite facies has caused extensive conversion of pyrite to pyrrhotite. Plastic deformation and remobilization of the sulfide ores has probably yielded a preferential enrichment of the more plastic minerals, especially chalcopyrite and sphalerite."
Geology of the copper-zinc deposits of stall lake mines lts., snow lake area, n. manitoba
C. J. A. Coats, L. A. Clark, R. Buchan, and J. J. Brummer
Economic Geology; December 1970; v. 65; no. 8; p. 970-984;


Cordierite
Canada
Manitoba, Ruttan Lake, Ruttan Mine

Cordierite, robust crystals to 1.2 cm© Rob Lavinsky


The cordierite from here was found in a strongly chloritizated rocks near the ore bearing formation. The area is metamorphosed to high greenschist, low amphibolite facies. I expect that the cordierite from here is not as good as the cordierite found further north at the Stall Lake Copper Mine. I am inclined to remove this location from the best minerals section, but as for now (2010) the image above is the only Manitoba cordierite in the database.

Cordierite
Germany
Baden-Württemberg Black Forest, Murg Valley, Wickartsmühle Quarry ,
Baden-Württemberg Black Forest, Zastlertal, Zeigerhalde ,

In the southern Black Forest, Baden-Württemberg, Germany high-temperature paragneisses (anatectic, with broad quartz-feldspar leucosomes) do occur at several localities. In the Murg Valley (especially at Wickartsmühle Quarry near Rickenbach) and at the Zeigerhalde, Zastlertal (Zastler Valley), Oberried near Freiburg blueish grey, fresh cordierite does occur, xls of 2 cm to 4 cm (Zeigerhalde) are known, being prismatic and showing pseudohexagonal forms. Most of the cordierite in the rock, making up up to 30 % of it, is weathered to grey clay minerals unfortunately.
( Sebastian Möller, 2009)


Cordierite
Germany
Rhineland-Palatinate, Eifel Mts ,

The Eifel area lies in Western Germany, near the borders to Belgium and Luxembourg. This region is one of the most interesting areas in Europe for collectors of microcrystals. This is due to relatively recent tectonic events (the last 430.000 years), leading both to rifting and volcanic activity. A large number of vulcanoes are in the area, with the Laacher See(13000 years old) as the youngest. An annual landlift of 1-2mm shows that the area is still active.

168 different localities are recorded in Mindat, listing an astonishing 435 different minerals. Cordierite is identified in 21 of of the locations, and the Caspar Quarry also carries the closely related minerals sekaninaite and possibly also indialite ( "indialite is questionable for the volkanic Eifel, also from the Bellerberg!" Günter Blass-2009 ).

The most important reason for all the different mineral species is that the vulcanoes has carried rock fragments (xenoliths) from low down in the crust and/or upper mantle to the surface. The minerals are found in voids in these xenoliths. Since the vulcanic activity takes place in the middle of a continent, the crust is thick and a lot more diversified than for a oceanic rift, giving a more diversified chemical environment for formation of minerals. It also helps that the vulcanic activity is relatively recent, so that the minerals has not been altered. Cordierite has consequently been formed at high temperatures and pressures quite far down in the crust and then been transported to surface in xenoliths embedded in the lava flows.

Based on the photos uploaded to Mindat, cordierite is found as well crystallized and unaltered reddish brown crystals to a few mm in size. Cordierite occurs in thermometamorphic shale or clay xenolites fallen into the basanitic lava flows, usually together with sanidine. Other minerals can be sillimanite or corundum. (Sebastian Möller, 2009)


Corderite
Germany
Rhineland-Palatinate, Eifel Mts, Andernach, Nickenich, Nickenicher Weinberg Mt. (Nickenicher Sattelberg Mt.)

Cordierite, FOV 4 mm© Stephan Wolfsried
Cordierite, 1.2 mm w/ purple Mullite© Chinellato Matteo


Corderite
Germany
Rhineland-Palatinate, Eifel Mts, Mayen, Ettringen, Bellerberg volcano, Caspar quarry

Cordierite xl 3.28 mm© Chinellato Matteo


I have included two locations of cordierite from this region. Further information on these and/or similar locations will be highly appreciated, as will general comments on the area.


Cordierite
India
Tamil Nadu, Chennai (Madras), Coimbatore District

Cordierite is a rockforming mineral, and it is a constituent of many of the rocks in the region. An almost 1000 km long mountain range methamorphosed to granulite facies in the Pan-African Orogeny some 550 mill years ago is the backbone of the Tamil Nadu geography and geology. It is therefore quite likely that cordierite may be found many places in this area. The only reference I have found to gem cordierite is Kiranur, a roughly 4 1/2 hr drive from Coimbatore, but this is not considered "rich enough for working" by the Geological Survey of India, I will not include this locality in the final draft of this article. I will keep this entry as a placeholder in case someone can add more information on this or other locations for cordierite in India


Cordierite
Italy
Sardinia, Oristano Province, Marrubiu, Mt. Arci, Funtanafigu Quarry

Cordierite FOV 7mm, crystal 2mm©


Small (mm sized) crystals of cordierite can be found in cavities in rhyolittic lava flows in this large quarry. At it's moderate age of 2-4 mill years, Mt Arci is the youngest volcano on Sardinia.


Cordierite
Italy
Tuscany, Grosseto Province, Roccastrada, Roccatederighi

Cordierite, crystal 3,6 mm© Enrico Bonacina
Cordierite crystal 0,5cm© 2009, JGW

" I would like to point also the interesting occurrence of cordierite crystals in southern Tuscany, Italy, spreaded into the magmatic materials of Roccastrada – Roccatederighi, Grosseto Province. This cordierite has a magmatic origin, and it has a particular importance and meaning because its occurrence in these acid lavas is probably related with anatectic origin.

In Roccastrada-Roccatederighi area there are occurrences of rhyolitic lava domes and also of small exogenous estrusions of these magmas. One of the most “famous” rhyolite domes occours just near (and under) of the village of Roccatederighi. The rock is usually deeply altered, but there is still possible to recognize and find quartz, the sanidine (K-feldspar up to 10 cm!), biotite and less plagioclase. As accessory minerals in these lavas there are cordierite crystals, occurring as euhedral-subhedral up to anhedral crystals, generally not greater than 15-20 mm and mostly altered more or less deeply, into pinite which gives to them a greenish, brownish coating. However I have seen specimens with small xls (not more than 4 mm) still “fresh” showing a pale violet colour.

These rhyolitic rocks are very interesting just for the presence of cordierite, which it is index of a peraluminous character really similar with most of monzogranites and the other rhyolites (of our so called "Tuscan Magmatic Province”) all highly Al rich and suggesting an anatectic origin , for fusion of probably meta-sedimentary previous rocks. "
Marco Barsanti- 2010.

Cordierite
Ivory Coast
"South West towards the Liberia border"

Stephane Mouthon posted some really interesting self found specimens from the Ivory Coast. There are very limited information on the net on the geology of the Ivory coast in general and cordierite in particular. It has therefore been a pleasant surprise to add this locality to the best mineral article of cordierite.

"Cordierite area is West/South, near Liberia border.
I find :
_ brown, yellow, colorless in clay migmatite area
_ deep blue in 'tardimigmatitic' granit, and always with some Sillimanite and Magnetite in the same area, but not in clay.

But crystals are rare, more chance with the blue cordierite.
Brown cordierite i can find some columnars pieces, but usually altered and disseminated
in clay in granular or pieces." Stephane Mouthon, 2010

Cordierite
Japan
Honshu Island, , Kinki Region, Kyoto Prefecture, Kameoka City

Cordierite/indialite ~19cm© Michael Roarke
Cordierite/indialite FOV 2.4mm© Andrew Tuma

Kameoko is the best location of sakura ishi (cherry blossom stones), or muscovite pseudomorphs after cordierite. The name sakura ishi comes from the six-sided trapiche structure of the crystals, giving a flower-like appearance some of which are partly or fully replaced by mica. The crystals can be found as porphyroblasts in a fine grained hornfels, and can often be found as complete barrel shaped crystals whethered free from the host rock. The hornfels is found in the contact zone between mud and chert sediments penetrated by a granite melt 98 mill years ago.

The trapiche pattern is formed by a complex intergrowth between cordierite and indialite crystals, where indialite forms the dark "flower core" , and cordierite the "flower leafs". Unaltered crystals can be found near Kyoto in unaltered hornfels.

The crystals can easily be cleaved perpendicular to their long axis to expose the internal hexagonal pattern. The hornfels can be very friable, as are the sakura ishi, which makes it easy to find nice crystal sections but difficult to collect matrix specimens Matrix specimens can be partly stabilized by glue impregnation. Many local collectors paint a solution of warm water and wood glue on the specimens; it quickly penetrates the porous hornfels.


Cordierite
Madagascar
Tuléar (Toliara) Province, Androy, Tsihombe

Cordierite, a gemmy, pleochroic 8 mm cut & polished cube.© Michael C. Roarke

The central and eastern part of the Tuléar province consists of highly metamorphosed rocks originating from the Pan African orogeny1. It is the same geological event that created the cordierite bearing rocks of India and Tanzania as well. Cordierite is found in cordierite-bearing gneisses with high Al and Mg content as grains or nodules, sometimes of sufficient size and clarity to be interesting for gem cutters and mineral collectors. Six cordierite locations are listed in Mindat, but there are probably several more.

"Correct locality for cordierites from Madagascar is Tsihombe area. Cordierites occur at big area but from mines around this town comes from majority of gem specimens." Tomasz Praszkier 2009.


1Pan-African Orogeny, A Kröner, Universität Mainz, Mainz, Germany, R J Stern, University of Texas-Dallas, Richardson TX, USA
2005


Cordierite
Norway
Telemark, Kragerø

Cordierite, 6.0 x 4.5 x 3.6 cm© Conny Larsson
Cordierite, "Star of Krageroe" (10.43 ct)© Jan Kihle

The Bamble sector contains highly methamorphosed rocks from the SvecoNorwegian Orogeny some 1200 mill years ago.These locations are all from the same cordierite bearing gneiss horizon that surface in irregular intervals and the occurance of cordierite was first described by Holm ( 1824), and several outcrops carrying similar looking cordierite are known, I will just mention a few. In this area, both crystals, pseudomorphs and gem quality cordierite may be found.

Head sized nodules of nicely coloured cordierite are known from outside Kragerø. Nicely coloured, "large" nodules and pseudohexagonal crystals (multiple cm size) are described from several locations in Bamble, Tvedestrand and Søndeled. The crystals may sometimes a have very sharp outline, but are normally partly altered to chlorite, muscovite or other minerals. Several good specimens can be found in museum collections, and probably also in private collections.

"The cordierite with hematite inclusions can be cut into beautiful gems, these are known as Blood-shot eye's to a gemmologist and in the gem trade. I have cut many myself which I found in the Kragero area in the late 1970s." 2009
Spencer Ivan Mather

Corderite
Norway
Telemark, Bamble (Bamle)

Talc after cordierite, xl is 2cm tall© Knut Eldjarn

Corderite
Norway,
Aust-Agder, Risør, Søndeled


Cordierite 5 cm crystals picture shows from "in situ" to specimen© Jan Kihle

Cordierite 5 cm crystal© Jan Kihle

Cordierite 5 cm crystal© Jan Kihle
Cordierite 5 cm crystal© Jan Kihle



"A discrete find of partly unaltered, sharp euhedral, aquamarine blue colored cordierite crystals up to 10 cm was made during the fall 2012 in the Bamble sector, Norway. " The crystals was found embedded in quartz with several other Mg/Al minerals. These specimens are about as good as anyone can imagine a cordierite specimen.


Corderite
Norway
Aust Agder, Akland

1,5cm cordierite©
2cm cordierite in quartz© olav revheim

Cordierite has been known from Akland a long time. During road construction work in 2002/2003 two cordierite bearing sections were exposed for a while. In one section, cordierite occured as large (up to 50cm) nodules of skyblue cordierite in white quartz. Occationally rounded pseudohexagonal crystals, sometimes fresh and sometimes with a thin light green alteration rim, could be found. In this section, gem grade material was rare. The other section was a sillimanite bearing mica rich gneiss/micaschist also bearing cordierite nodules. Here the color was more violet blue, and the nodules were frequently altered to a chlorite/mica mixture, gem sections were not uncommon. Occationally, small hematite inclusions colored the cordierite brownish red and created a nice "sunstone" effect similar to that observed in feldspar. Large sections of this material combining the brownish red "cordierite sunstone", violet blue cordierite and light green "pinite" has been polished. Setesdalen Mineralpark has a large slap exceeding 1 sq.m. displayed.


Cordierite
Sweden
Närke, Askersund, Västerby

"Pinite" after cordierite,15 x 10.6 x 9.3 cm © Rob Lavinsky



Cordierite
Tanzania
Manyara Region, Babati District, Babati

Cordierite, a 1.8 cm tall dichroic fragment© JSS


Tanzania is also one of the frequently noted cordierite gem locations and the origin is highly metamorphosed rocks from the Pan African Orogeny. The economical and mineralogical importance of cordierite seems to be too small for anyone but petrologists to make any note of the occurances, but based on the geological setting, there should be several cordierite locations in Tanzania.


Cordierite
USA
New Hampshire, Cheshire Co, Richmond

Cordierite, 12.1 x 8.2 x 4.6 cm © Rob Lavinsky
Cordierite, 12 x 10 x 7 cm © Rob Lavinsky

Cordierite is a quite common mineral in the metamorphic rocks in New Hampshire, but really great crystals are only reported from the Richmond Soapstone Quarry near Richmond. I have not been able to find much information on this quarry, but some information can be found in "The geology of New Hampshire, part III Minerals and mines" by T.R.Meyers and Glenn W.Stewart, 5th reprint. They quote information from Hawes, George W. (1878) sying that "very fine specimens of this beautiful mineral" was found at the opening of the quarry. These crystals where apparantly beautiful blue crystals in a quartz matrix from a mica schist. It seems like the brownish crystals uploaded to mindat.org are from a find in the 1970-ties.

I've com about as far as I can for now. Thank you all for valuable help and contribution.
[Olav Revheim 2010]



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Edited 20 time(s). Last edit at 04/12/2013 12:25PM by Olav Revheim.
avatar Re: Cordierite
December 05, 2009 11:58PM
Bob Southern

Gents
I've attached three photos of some Cordierite. They are from the # 4 Orebody, 3341 Stope Alteration Zone of the now defunct Stall Lake Copper Mine,
in Snow Lake, Manitoba, Canada.
The orebody here was a Volcanic rock associated, Stratabound Massive Sulphide Type Deposit. The mines depth went to over 4000 feet. Cordierite crystals up to 0.6 m long
and 15 cm in diameter had been seen with Chlorite reaction rims in the Alteration Zone during mining operations.
Photo Cordierite 3 - Massive Cordierite with Pyrrhotite, Pyrite, Chalcopyrite rinds. Shows slight crystal form at bottom right & upper middle left. 22 cm x 23 cm x 9 cm
Photo Cordierite 2 - Opposite side of previous.
Photo Cordierite 4 - 4.5 cm x 4.5 cm x 3.5 cm crystal protruding from Pyrite, Pyrrhotite, Chalcopyrite matrix. Specimen size - 13 cm.

Thought I'd share these
Bob

Olav,
I'll look into getting as much info and photos as i can for the Manitoba, Canada occurrences. The Ruttan Mine is close by, and I know some people that worked there also.
I'll set up to upload photos this week.
Cheers
Bob

"If it can't be grown it's gotta be mined. "

Rock Currier
Crystals not pistols.



Edited 1 time(s). Last edit at 12/06/2009 12:00AM by Rock Currier.
avatar Re: Cordierite
December 06, 2009 12:01AM
Philippe M. Belley

Manitoba has some insanely nice/large cordierite crystals. Geco mine, Ontario [www.mindat.org] has produced very fine gem material.

Rock Currier
Crystals not pistols.
avatar Re: Cordierite
December 06, 2009 12:02AM
Hello,

As to the Eifel Mts., the Bellerberg Locality is a very good choice. There have been at least two articles in Lapis (in German language), one is about pleochroitic, perfect, but small xls, the other about the locality in general.

The mineral occurs in thermometamorphic shale or clay xenolites fallen into the basanitic lava flows, usually together with sanidine. Other minerals can be sillimanite or corundum.


In the southern Black Forest, Baden-Württemberg, Germany high-temperature paragneisses (anatectic, with broad quartz-feldspar leucosomes) do occur at several localities. In the Murg Valley (especially at Wickartsmühle Quarry near Rickenbach) and at the Zeigerhalde, Zastlertal (Zastler Valley), Oberried near Freiburg blueish grey, fresh cordierite does occur, xls of 2 cm to 4 cm (Zeigerhalde) are known, being prismatic and showing pseudohexagonal forms. Most of the cordierite in the rock, making up up to 30 % of it, is weathered to grey clay minerals unfortunately.

Another German locality is Silberberg Mt., Bodenmais, Bavarian Forest, Bavaria. There metamorphic rocks with pyrrhotite ore bodies do occur, containing cordierite. Some had gem grade iolite.

Regards,
Sebastian Möller

Rock Currier
Crystals not pistols.
avatar Re: Cordierite
December 06, 2009 12:04AM
Olav Revheim

Bob,

This information, as well as the photos, and of course the specimens are absolutely great. Just what we're after. Not only the cordierite, but also the association with the sulfides is amazing. I found a few articles on the general geology and mining history of the area, and I'll fill in a little bit more on the geology in due time.

I have added cordierite to the mineral list for Stall Lake Copper mine, and used your message here as reference for the entry.

I would really appreciate if you can elaborate a little bit on the cordierite finds in this mine.

- Do you if many specimens were saved, or just a few?
- Was cordierite frequently found ? or was this a one off?
- Are these specimens represented in any museums or public displays?


Also I would like to ask for another favor:

Can you upload the photos onto the webpage?

The procedure is as follows:
- Find the location page
- Press the add photo "button"
- Upload the photo from your computer
- Fill in the requested information.

I cannot ( I think) use photos that are attached to messages, only those uploaded to the photo gallery. Also it would be fantastic if you can take a close-up of the crystal in the lower right corner of the specimen pictured in your image "cordierite-3.jpg".



Thanks & regards

Olav

Rock Currier
Crystals not pistols.
avatar Re: Cordierite
December 06, 2009 12:05AM
Bob Southern [ PM ]
Re: Cordierite
October 25, 2009 10:02PM IP/Host: thsnmb01dc1-200-92.dynamic.mts.net
Registered: 3 months ago
Posts: 9
Olav,
I'll look into getting as much info and photos as i can for the Manitoba, Canada occurrences. The Ruttan Mine is close by, and I know some people that worked there also.
I'll set up to upload photos this week.
Cheers
Bob

"If it can't be grown it's gotta be mined. "

Rock Currier
Crystals not pistols.
avatar Re: Cordierite
December 06, 2009 12:06AM
Olav Revheim [ PM ]
Re: Cordierite
October 31, 2009 03:13PM IP/Host: cC8264BC1.dhcp.bluecom.no
Registered: 3 years ago
Posts: 115
I am slowly working my way through the cordierite locations in the "best minerals" article and have put together a preliminary draft for the Eifel region in Germany. I'd appreciate any suggestions/corrections to the text as it is now.

Any help will be appreciated.

Thanks

Olav

Rock Currier
Crystals not pistols.
avatar Re: Cordierite
December 06, 2009 12:07AM
Sebastian Möller [ PM ]
Re: Cordierite
November 14, 2009 04:13PM IP/Host: Q12e2.q.pppool.de
Registered: 1 year ago
Posts: 502
Hello,

As to the Eifel Mts., the Bellerberg Locality is a very good choice. There have been at least two articles in Lapis (in German language), one is about pleochroitic, perfect, but small xls, the other about the locality in general.

The mineral occurs in thermometamorphic shale or clay xenolites fallen into the basanitic lava flows, usually together with sanidine. Other minerals can be sillimanite or corundum.


In the southern Black Forest, Baden-Württemberg, Germany high-temperature paragneisses (anatectic, with broad quartz-feldspar leucosomes) do occur at several localities. In the Murg Valley (especially at Wickartsmühle Quarry near Rickenbach) and at the Zeigerhalde, Zastlertal (Zastler Valley), Oberried near Freiburg blueish grey, fresh cordierite does occur, xls of 2 cm to 4 cm (Zeigerhalde) are known, being prismatic and showing pseudohexagonal forms. Most of the cordierite in the rock, making up up to 30 % of it, is weathered to grey clay minerals unfortunately.

Another German locality is Silberberg Mt., Bodenmais, Bavarian Forest, Bavaria. There metamorphic rocks with pyrrhotite ore bodies do occur, containing cordierite. Some had gem grade iolite.

Regards,
Sebastian Möller

Rock Currier
Crystals not pistols.
avatar Re: Cordierite
December 06, 2009 12:08AM
Peter Haas [ PM ]
Re: Cordierite
December 01, 2009 05:06PM IP/Host: p54ABC65A.dip.t-dialin.net
Registered: 3 years ago
Posts: 2,098
Rock,

There also are several good cordierite localities in a small area within the French Massif Central. I will ask for help in the French forum.

Rock Currier
Crystals not pistols.
avatar Re: Cordierite
December 06, 2009 12:08AM
Spencer Ivan Mather [ PM ]
Re: Cordierite
December 02, 2009 12:22PM IP/Host: cpc1-yarm2-0-0-cust652.pete.cable.ntl.com
Registered: 3 months ago
Posts: 72
The cordierite with hematite inclusions that Knut Eldjern is talking about can be cut into beautiful gems, these are known as Blood-shot eye's to a gemmologist and in the gem trade. I have cut many myself which I found in the Kragero area in the late 1970s.

Spencer

Rock Currier
Crystals not pistols.
avatar Re: Cordierite
December 06, 2009 12:09AM
Guenter Blass [ PM ]
Re: Cordierite
December 02, 2009 01:04PM IP/Host: xdsl-78-35-136-233.netcologne.de
Registered: 9 months ago
Posts: 5
H Rock,

please correct "related minerals sekianinite " to sekaninaite! And indialite is questionable for the volkanic eifel, also from the Bellerberg!

regards
Günter Blass

Rock Currier
Crystals not pistols.
Re: Cordierite
December 06, 2009 04:17PM
I have posted several photos of self-collected cordierite crystals, many from the Richmond, NH locality, on my New Hampshire mineral species web site.
This link will take you directly to the cordierite gallery: [www.mindatnh.org]

Tom Mortimer
avatar Re: Cordierite
December 06, 2009 05:07PM
pl    
Correct locality for cordierites from Madagascar is Tsihombe area. Cordierites occur at big area but from mines around this town comes from majority of gem specimens.

Tom

-------------------------------------
"Spirifer" Geological Society
avatar Re: Cordierite
December 06, 2009 06:21PM
de    
Hello,

I've added the Zeigerhalde Locality. The Murg Valley localities I will add the next days, the Eggberg locality, too. These are only a few out of about 50 localities in that area I have read of.

Regards,
Sebastian Möller
avatar Re: Cordierite
July 09, 2010 09:22PM
ci    
Hi

If i can suggest a locality, Ivory Coast (West Africa) have some cordiérite, brown, blue and colorless.
Rarely crystals, more granular, massive, columnar etc etc.
I find it myself.

I dont know if you are interested by some pictures, just to know that in this part of West Africa, you can find it.

See you.
avatar Re: Cordierite
July 09, 2010 11:13PM
Stephane,

Yes, we would be glad to know about a locality for Cordierite in the Ivory Coast. Can you tell us something about it? Just were in the Ivory Coast is it? Can you tell us something about the geology of the locality? Is the locality worked only for Cordierite or are other minerals found with it? Can you supply some pictures of it and the locality perhaps?

Rock Currier
Crystals not pistols.
avatar Re: Cordierite
July 10, 2010 12:08AM
ci    
First, sorry for my level, i will try to give 'basic' information.
It's just personal finding, i go to the bush and try to find always some news species, not listed for this country.
For this reason, better to speak about 'indice' than industrial or commercial possibility.
Cordierite area is West/South, near Liberia border.
I find :
_ brown, yellow, colorless in clay migmatite area
_ deep blue in 'tardimigmatitic' granit, and always with some Sillimanite and Magnetite in the same area, but not in clay.

But crystals are rare, more chance with the blue cordierite.
Brown cordierite i can find some columnars pieces, but usually altered and disseminated
in clay in granular or pieces.

1st and 2nd picture, brown/blue , the same stone
3rd, blue/yellow

You can delete the pictures if it's too bad.
Attachments:
open | download - DSC02878.JPG (43.9 KB)
open | download - DSC02875.JPG (36.9 KB)
open | download - DSC02692.JPG (46.2 KB)
avatar Re: Cordierite
July 10, 2010 05:52AM
Stephane,
It certainly looks like you have found Cordierite. More than that it looks like you have found what would be called "gem grade" variety that is called Iolite or sometimes watter sapphire. This is the kind of material that has a high value to those who cut gems, especially if it will cut clean stones larger than more than a few carats each. Well formed crystals of Cordierite are rare from any locality and I don't think I have ever seen a really sharp one. We would like to know if possible exactly where this material comes from, but I should caution you that to publicly give the exact locality here may cause a number of people to immediately go there and try and buy the material, so at least until you know where you stand you might be wise to just give us the name of the region that it comes from. This is the kind of thing that is ideally suitable to small scale mining by the locals and can create mini gem rushes where hundreds of men will flock to the area to try their luck in finding gems. It is possible that this has already happened or is happening? Did you actually dig the specimens you picture or did you buy them from some of the locals who had already dug them and knew something of their value.

It sound as though you have had some training in geology. Is this the case? As far as this web site is concerned, The Ivory Coast is a big blank spot in the map. We have only one specimen shown for the Ivory Coast and that is a diamond with no further locality information than just Ivory Coast. Any information that you can give us or pictures that you can send us would be much better than we have now. If you would like to upload pictures of minerals from the Ivory Coast and or surrounding countries, I will raise your level to a level 1 member of mindat so you can do it yourself. I would encourage you to do this.

Rock Currier
Crystals not pistols.
avatar Re: Cordierite
July 10, 2010 08:17AM
ci    
All the stones are personal finding (the same for the white fluorescent stones).

Not at all training in geology or gemmology (i m graduate in business shool, not the same training), but when you have a passion, nothing can stop you...and litterature, website and museum can give you enough information if you are really motivated.
I m collector till the age of 14, but now i need to have an Ivorian collection species, and when you find yourself the stones,
i can tell you that is for me a real pleasure, and original collection.

I give information about the area, i can't be more precise.

"I will raise your level to a level 1 member of mindat " that 's really nice, i don't know if i can have this honor.

You can contact me in PM, if you need more informations.

See you.
avatar Re: Cordierite
July 10, 2010 12:01PM
Stephane,
You are now a level one and you can upload pictures and make locality changes in the database. If you need instructions on how to upload pictures let me know and I can tell you how to do it. You should also read the Mindat Manual that you can access from one of the menu buttons on the left side of the Mindat home page.

Rock Currier
Crystals not pistols.
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