Cronstedtite

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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?



Cronstedtite
Fe₂⁺²Fe³⁺[(Si,Fe³⁺)₂O₅](OH)₄ trigonal



Cronstedtite is not a common mineral but it is not extremely rare and Mindat lists 37 localities (2010). It was recognized as a species since about 1890. By far the best locality for specimens appears to be the Herja mine in Romania. Many of the fine specimens from this mine have suffered disintegration of their sulfide matrix and large specimens (larger than 5cm0 are very rare because they have mostly fallen apart. The mineral itself appears to be stable.
[Rock Currier 2010]



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

Cronstedtite 4.5cm wide	© Alfredo Petrov

Cronstedtite
France
Languedoc-Roussillon, Carcassonne, Aude, Mas-Cabardès, Salsigne, Salsigne mine




Cronstedtite
Germany
Saxony-Anhalt, Harz Mts, Gernrode

Cronstedtite FOV 6mm	© Thomas Witzke

Cronstedtite
Peru
Huánuco Department, Dos de Mayo Province, Huallanca District, Huanzala Mine

The mineral is rather rare at Huanzala. Of about 20 trips made to Peru to buy minerals I saw only one good specimen of about 15cm. The Cronstedtites were growing thickly crusted on a matrix of pyrite crystals and looked similar to the material from Romania pictured below, but a bit blacker. For a while it was probably the best specimen of Cronstedtite produced in the southern hemisphere, but the pyrite eventually disintegrated and only a few TN and micro specimens remain now. Ill try and get a picture of them to post here.
[Rock Currier 2010]


Cronstedtite
Romania
Maramures Co., Baia Mare (Nagybánya)




Cronstedtite
Romania
Maramures Co., Baia Mare (Nagybánya), Herja Mine (Kisbánya)

Cronstedtite, 3.5cm wide	© Rob Lavinsky

The mine is near the village of Chuizbaia. Kisbánya was the old Hungarian name for this village. The Cronstedtites from this old locality have yet no rivals. The look almost black but are really almost an dark azurite blue. They are frequently found growing on little brown bladed siderite crystals which is typical if not unique for this locality. The specimens from this locality are usually found growing on a sulfide matrix that over time has proven to be not stable and most of the great specimens from this locality have fallen apart. Specimens over 5cm are quite rare. I know of only two great ones in the United States and one of those may have disintegrated. Martin Stevko comments: "I saw this specimen from Philadelphia Academy of Scieneces presonally and I remeber that it was superb. Also I have personal experience with cronstedtite decomposing. Also specimens from Herja tend to by unstable, because matrix of these specimens usually contain pyrite. I saw in old collections also cronstedtites from other localities (Kutná Hora, Příbram) a these are also unstable. In the Los Angeles area I only knew of one nice small Cronstedtite from this locality, but over the years it also fell apart.
[Rock Currier 2010]


Cronstedtite
Spain
Murcia, Sierra de Cartagena, La Unión, Brunita Mine


Cronstedite
United Kingdom
England, Cornwall, Camborne - Redruth - St Day District, Gwennap area, Wheal Jane, Baldhu




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Rock Currier
Crystals not pistols.



Edited 10 time(s). Last edit at 07/25/2010 07:36AM by Rock Currier.

Hello,

Concerning the locality Gernrode, Hartz Mts., Germany: The exact locality is Hohe Warte Mine, see here.

There is another good locality: Kutna Hora, Bohemia, Czech Republic. There cronstedtite appears as greenish black prismatic xls up to about a cm. I will look at the literature what I can find about those.

Regards,
Sebastian Möller

In Cornwall, Wheal Jane produced good ones.

Peter, I have added the picture of the best specimen we have in the mindat gallery and the locality to the Cronstedite article. Thanks for the suggestion. Do you know anything about the locality and the cronstedites from there? How much better do they get?

Rock Currier
Crystals not pistols.

Hello,
As Sebastian mentioned, good cronstedtite specimens were found also at Kutná Hora (crystals up to 1 cm) in
Czech Republic. Nice but very rare are old cronstedtite specimens from Příbram (type locality of cronstedtite).
Here was found in 1817 at stope between 5. and 6. level of the Vojtěch vein as black acicular crystals up
to 2 cm embed in white calcite with pyrite. This was one time find and cronstedtite in Příbram was never
found again, thus specimens from this locality are exceedingly rare and are usually confused with specimens
from Kutná Hora which are far usual.
Sincerely

Martin

Martin, Thats quite interesting. Do you see any cronstedites that we have pictured in the article that may be from that old find at Pribram? Can you give us a literature reference to that famous old find?

Rock Currier
Crystals not pistols.

Hello Rock,
Unfortunatelly photos of cronstedtite from Příbram are rare, because 99% percent of cronstedtite
specimens from Příbram are held by institutional collections. Cronstedtite from Příbram was first
described by Steinmann (1821). Klavaňa (1886) in his book about minerals of the former Czech
kingdom and Kadečka (1878) in his notes about Příbram deposit described that cronstedtite in
Příbram was found in 1817 at stope between 5. and 6. level of the Vojtěch vein at Vojtěch (Adalbert)
shaft. Later searching of cronstedtite on same place proved to by unsuccessful (Kladečka, 1878).
I think that good cronstedtite specimen from Příbram is far rare as good one from Herja Mine in
Romania, but specimens from Herja are still far better as Příbram cronstedtites.

Martin, Thanks for the useful information. It will find its way into the Best Minerals article on Cronstedite.

Rock Currier
Crystals not pistols.

Two localities have produced really good cronstedtites in Bolivia:

Potosi Department, Llallagua: I see Rock already included a couple photos of these for the article. This mineral has been known from Llallagua for many decades already, and batches still come out once in a while. Beware the ones on an amorphous brown matrix - it tends to dehydrate and crumble with time (but then at least you get nice micromounts :)

Oruro Department, Huanuni mine: Only one large lot (that I'm aware of), and it was mined in the early 1990s. Long prismatic crystals, instead of tabular like the Llallagua cronstedtites. None of the miners or mine engineers knew what they were - Some thought tourmaline, because of the triangular cross-section, others tried to sell them as a weird variety of vivianite, because of the bluish streak. who knows where they all ended up... probably scattered in collections in Bolivia and around the world with bad labels.



Edited 1 time(s). Last edit at 07/14/2010 01:05AM by Alfredo Petrov.

The photo from Hunan, Bolivien (probably Huanuni) in "Mineralien Enzyklopädie" from Petr Korbel and Milan Novák shows more like 6sided rounded Prisms.
The same as that from Pribram, Böhmen in "Der Kosmos-Mineralienführer" J. Bauer
But the photos are not very good.

Milo

Emil,
We would welcome better images.

Rock Currier
Crystals not pistols.