http://www.mindat.org/msgboard-69.html Sat, 28 Nov 2009 01:05:58 +0000 Phorum 5.2.8-RC1 http://www.mindat.org/forum.php?read,69,155691,160272#msg-160272 http://www.mindat.org/forum.php?read,69,155691,160272#msg-160272
I've embedded the information you gave into the article. It seems like none of these locations has been entered to the localities database, which I think they should. I don't dare to add them myself as I would most likely make a mess of the hirarchy of the Black Forest locations.

I think I have come as far as I can with the article for now. I'll appreciate further help to improve the article. I'd love to have more information on Richmond NH locality in the US in particular, but any added information will be highly appreciated...

Olav

PS! Rock, Thanks for all help and encouragement.]]> Olav Revheim Best Minerals C Sun, 15 Nov 2009 21:13:57 +0000 http://www.mindat.org/forum.php?read,69,155691,160174#msg-160174 http://www.mindat.org/forum.php?read,69,155691,160174#msg-160174
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]]> Sebastian Möller Best Minerals C Sat, 14 Nov 2009 16:13:47 +0000 http://www.mindat.org/forum.php?read,69,155691,158306#msg-158306 http://www.mindat.org/forum.php?read,69,155691,158306#msg-158306 Rock Currier Best Minerals C Sun, 01 Nov 2009 12:02:38 +0000 http://www.mindat.org/forum.php?read,69,155691,158304#msg-158304 http://www.mindat.org/forum.php?read,69,155691,158304#msg-158304
Thanks for the information and support. Manitoba is in there, and I am really intrigued by the specimens Bob Southern has attached in his first posting. I've also added the Geco mine.

I'll definately dig into both locations to see what kind of information I can find. Cordierite has been more difficult and time consuming than I thought it would be, but I'll take one location at the time. Everyones help and suggestions are highly appreciated.

thanks
Olav]]> Olav Revheim Best Minerals C Sun, 01 Nov 2009 11:16:51 +0000 http://www.mindat.org/forum.php?read,69,155691,158288#msg-158288 http://www.mindat.org/forum.php?read,69,155691,158288#msg-158288 I know little about Cordierite or the Eifel locality and nothing at all about the Cordierite from there. Hopefully someone on mindat can give you the guidance you are looking for. But Philippe's locality of the Geco mine should be included. I have a nice gemmy piece from there that I can perhaps take a picture of and upload that shows the nice color change. I at one time went through the town of Manitouwadge and bought some nice pieces of gemmy Cordierite from the sample man there and have a great story about how abundant the material was underground.]]> Rock Currier Best Minerals C Sun, 01 Nov 2009 03:00:57 +0000 http://www.mindat.org/forum.php?read,69,155691,158237#msg-158237 http://www.mindat.org/forum.php?read,69,155691,158237#msg-158237 www.mindat.org] has produced very fine gem material.]]> Philippe M. Belley Best Minerals C Sat, 31 Oct 2009 15:37:28 +0000 http://www.mindat.org/forum.php?read,69,155691,158235#msg-158235 http://www.mindat.org/forum.php?read,69,155691,158235#msg-158235
Any help will be appreciated.

Thanks

Olav]]> Olav Revheim Best Minerals C Sat, 31 Oct 2009 15:13:44 +0000 http://www.mindat.org/forum.php?read,69,141984,157917#msg-157917 http://www.mindat.org/forum.php?read,69,141984,157917#msg-157917 Rock Currier Best Minerals C Wed, 28 Oct 2009 02:42:56 +0000 http://www.mindat.org/forum.php?read,69,141984,157873#msg-157873 http://www.mindat.org/forum.php?read,69,141984,157873#msg-157873 Ron Crouse Best Minerals C Tue, 27 Oct 2009 17:12:44 +0000 http://www.mindat.org/forum.php?read,69,155691,157679#msg-157679 http://www.mindat.org/forum.php?read,69,155691,157679#msg-157679 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]]> Bob Southern Best Minerals C Sun, 25 Oct 2009 22:02:59 +0000 http://www.mindat.org/forum.php?read,69,141984,157647#msg-157647 http://www.mindat.org/forum.php?read,69,141984,157647#msg-157647 Besides that, many thousands tons of colemanite were used as B ore.

Of course shiny crystals and druses of them and also radial concretions covered by crystal terminations are known from Inder mines.]]> Pavel Kartashov Best Minerals C Sun, 25 Oct 2009 14:13:23 +0000 http://www.mindat.org/forum.php?read,69,155691,157622#msg-157622 http://www.mindat.org/forum.php?read,69,155691,157622#msg-157622 Its starting to look good.]]> Rock Currier Best Minerals C Sun, 25 Oct 2009 03:57:47 +0000 http://www.mindat.org/forum.php?read,69,141984,157621#msg-157621 http://www.mindat.org/forum.php?read,69,141984,157621#msg-157621 Rock Currier Best Minerals C Sun, 25 Oct 2009 03:54:29 +0000 http://www.mindat.org/forum.php?read,69,155691,157447#msg-157447 http://www.mindat.org/forum.php?read,69,155691,157447#msg-157447
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".

:)-D

Thanks & regards

Olav]]> Olav Revheim Best Minerals C Fri, 23 Oct 2009 21:06:39 +0000 http://www.mindat.org/forum.php?read,69,141984,157093#msg-157093 http://www.mindat.org/forum.php?read,69,141984,157093#msg-157093 Here [www.mindat.org] are some photos of colemanite xl from Inder. Remember that it isn't the largest or the best one, because it is from my collection, which isn't the largest or the best... :(]]> Pavel Kartashov Best Minerals C Wed, 21 Oct 2009 17:21:15 +0000 http://www.mindat.org/forum.php?read,69,155691,157013#msg-157013 http://www.mindat.org/forum.php?read,69,155691,157013#msg-157013 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]]> Bob Southern Best Minerals C Wed, 21 Oct 2009 02:52:52 +0000 http://www.mindat.org/forum.php?read,69,155691,156971#msg-156971 http://www.mindat.org/forum.php?read,69,155691,156971#msg-156971
(:P)

Olav]]> Olav Revheim Best Minerals C Tue, 20 Oct 2009 19:07:47 +0000 http://www.mindat.org/forum.php?read,69,137380,156107#msg-156107 http://www.mindat.org/forum.php?read,69,137380,156107#msg-156107 www.mindat.org] apparenly are the first ones of cassiterite from Iul'tin deposit...B)-
This is really strange, because it is the most significant in USSR object producing hundreds kg of cassiterite crystals!8-)]]> Pavel Kartashov Best Minerals C Wed, 14 Oct 2009 17:01:33 +0000 http://www.mindat.org/forum.php?read,69,137380,156067#msg-156067 http://www.mindat.org/forum.php?read,69,137380,156067#msg-156067 Ralph Bottrill Best Minerals C Wed, 14 Oct 2009 12:53:18 +0000 http://www.mindat.org/forum.php?read,69,137380,156049#msg-156049 http://www.mindat.org/forum.php?read,69,137380,156049#msg-156049 Matteo Chinellato Best Minerals C Wed, 14 Oct 2009 09:56:13 +0000 http://www.mindat.org/forum.php?read,69,137380,156045#msg-156045 http://www.mindat.org/forum.php?read,69,137380,156045#msg-156045 can you tell us a bit more about the deposit, the specimens etc (size, value, how common, etc)? See [www.mindat.org]]]> Ralph Bottrill Best Minerals C Wed, 14 Oct 2009 09:29:03 +0000 http://www.mindat.org/forum.php?read,69,137380,155872#msg-155872 http://www.mindat.org/forum.php?read,69,137380,155872#msg-155872 Rock Currier Best Minerals C Tue, 13 Oct 2009 11:03:21 +0000 http://www.mindat.org/forum.php?read,69,137380,155721#msg-155721 http://www.mindat.org/forum.php?read,69,137380,155721#msg-155721 Matteo Chinellato Best Minerals C Mon, 12 Oct 2009 04:34:35 +0000 http://www.mindat.org/forum.php?read,69,137380,155697#msg-155697 http://www.mindat.org/forum.php?read,69,137380,155697#msg-155697 Its always hard to know where to draw a line - Elba cassiterites could be the holy grail to some collectors?]]> Ralph Bottrill Best Minerals C Sun, 11 Oct 2009 23:24:50 +0000 http://www.mindat.org/forum.php?read,69,137380,155693#msg-155693 http://www.mindat.org/forum.php?read,69,137380,155693#msg-155693 Rock Currier Best Minerals C Sun, 11 Oct 2009 23:03:39 +0000 http://www.mindat.org/forum.php?read,69,155691,155691#msg-155691 http://www.mindat.org/forum.php?read,69,155691,155691#msg-155691


Cordierite
(Mg,Fe)₂Al₄Si₅O₁₈

Corderite 22cm wide	© Rob Lavinsky

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.

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 thin 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 cordierite 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] ). 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, and also 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.

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 4 sections, largest display size crystals, best gems, best microcrystals and best codierite pseudomorphs.

Cordierite
Brazil
Southeast Region, Minas Gerais, Coroaci, Virgolândia

Cordierite, etched floater 1.5x0.7x0.4 cm	© 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, as I am pretty much stuck on this location without help.

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.)

More information on this and/or similar locations will be highly appreciated.

Cordierite
Canada
Manitoba, Snow Lake, Stall Lake Copper Mine


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

More information on this and/or similar locations will be highly appreciated.

Cordierite
Canada
Manitoba, Ruttan Mine

Cordierite, robust crystals to 1.2 cm	© Rob Lavinsky

More information on this and/or similar locations will be highly appreciated.

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 sekianinite and indialite.

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)

Andernach, Nickenich,
Nickenicher Weinberg Mt. (Nickenicher Sattelberg Mt.)

Cordierite, FOV 4 mm	© Stephan Wolfsried

Ettringen, Bellerberg volcano, Ettringer Bellerberg Mt. (Bellberg Mt.; Bellenberg Mt.; Billenberg Mt.; Boilenberg Mt.), Caspar Quarry

Cordierite crystal of 3.28 mm	© Chinellato Matteo

I have included two locations of cordierite from this region, which may or may not be the best choices. 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

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 FOV 7mm, crystal 2mm	©

More information on this and/or similar locations will be highly appreciated.


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

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 appearence. 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/indialite intergrowths, FOV 24mm	© Andrew Tuma

Cordierite/indialite intergrowths, partly or fully replaced by mica 19 x 15 x 10 cm	© Michael C. Roarke

A great internet resource for these amazing crystals can be found at
[www.users.muohio.edu]

More information on this and/or similar locations will be highly appreciated.


Cordierite
Madagascar
Tuléar (Toliara) Province

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.

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

8 mm cut cube of pleochroic cordierite	© Michael C. Roarke

More information on this and/or similar locations will be highly appreciated.

Cordierite
Norway
Telemark, Kragerø
Telemark, Bamble
Aust Agder, Søndeled
Aust Agder, Tvedestrand

Cordierite, 6.0 x 4.5 x 3.6 cm	© Conny Larsson

Talc after cordierite, Bamble, size?	© Knut Eldjarn

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.

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.

More information on this and/or similar locations will be highly appreciated.

Cordierite
Sweden
Närke, Askersund, Västerby

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

More information on this and/or similar locations will be highly appreciated.


Cordierite
Tanzania
Manyara Region, Babati District, Babati

"1.8 by 1.0 cms piece of dichroic Cordierite	© 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.

More information on this and/or similar locations will be highly appreciated.


Cordierite
USA
New Hampshire, Cheshire Co, Richmond

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.

Cordierite, 12.1 x 8.2 x 4.6 cm	© Rob Lavinsky

" Cordierite, 12 x 10 x 7 cm	© Rob Lavinsky

More information on this and/or similar locations will be highly appreciated.]]> Rock Currier Best Minerals C Sun, 11 Oct 2009 23:01:24 +0000 http://www.mindat.org/forum.php?read,69,137380,155429#msg-155429 http://www.mindat.org/forum.php?read,69,137380,155429#msg-155429 www.mindat.org]]]> Matteo Chinellato Best Minerals C Sat, 10 Oct 2009 10:07:40 +0000 http://www.mindat.org/forum.php?read,69,137380,155427#msg-155427 http://www.mindat.org/forum.php?read,69,137380,155427#msg-155427 I am happy to put this in if you consider it an important occurrence with good specimens in many collections. I started this article for Australian cassiterites then expanded it to international sites. As a result some of the Australian sites may be not up to the international standard, or perhaps we should add more international locations? I am open to suggestions?]]> Ralph Bottrill Best Minerals C Sat, 10 Oct 2009 09:32:31 +0000 http://www.mindat.org/forum.php?read,69,137380,155297#msg-155297 http://www.mindat.org/forum.php?read,69,137380,155297#msg-155297 Matteo Chinellato Best Minerals C Fri, 09 Oct 2009 15:04:53 +0000 http://www.mindat.org/forum.php?read,69,137380,155254#msg-155254 http://www.mindat.org/forum.php?read,69,137380,155254#msg-155254 Rock Currier Best Minerals C Fri, 09 Oct 2009 11:27:51 +0000