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Improving Mindat.orgAragonite?

16th Feb 2015 00:47 UTCReiner Mielke Expert

http://www.mindat.org/photo-666738.html this looks like calcite to me. Why do you call it aragonite?

16th Feb 2015 03:42 UTCRalph S Bottrill 🌟 Manager

it does look like calcite, but look down the main prism axis and check the symmetry, Harry.

16th Feb 2015 04:36 UTCKeith Compton 🌟 Manager

HI

While not having a specimen I note that several well known dealers had these specimens listed as Aragonite some years back.

I would have imagined that they would have been relatively sure they were aragonite.

Cheers

16th Feb 2015 12:43 UTCUwe Kolitsch Manager

I tend to agree with calcite. Message sent.

16th Feb 2015 13:49 UTCReiner Mielke Expert

Hello Keith,

It is common practice to call anything that forms long prismatic crystals aragonite (as was the case with the ubiquitous mexican "aragonite" which is calcite), so I would not be surprised to find such things labelled as aragonite without any testing having been done.

16th Feb 2015 14:07 UTCThomas Lühr Expert

Hello all

Reiner, you are so right!

Such slender calcite crystals are often mislabeled as aragonite, regrettably - even by dealers. If there are separate crystals, like at the shown specimen, it's easy to distinguish aragonite from calcite by the cleavage: perfect at calcite, none at aragonite. A very simple method, I think.

At example I purchased this specimen -definitely a calcite- labeled as aragonite.

http://www.mindat.org/photo-361799.html

So I doubt that aragonite occurs at all at the Kohnstein quarry. May be the entry of Aragonite is erroneous and has to be deleted. Can someone confirm the occurrence of (actual) aragonite at this locality?

Best regards

Thomas

16th Feb 2015 15:13 UTCUwe Kolitsch Manager

Ref. for the aragonite entry says:

"NBMG Spec. Pub. 31 Minerals of Nevada"

"Replaced by calcite"

Hmmm...

16th Feb 2015 16:58 UTCDon Windeler

I'll have to say I've wondered a little about this question before.

The Northern Lights mine is in western Mineral County, just one range east of the Yerington in Lyon County. The Yerington District is known for the "cactus" calcites that came out years ago, maybe when Ananconda was operating the big pit west of the town. These look very similar to the Northern Lights material and I'm not sure why one is calcite and the other aragonite.

See Yerington calcites.

That said, I've not tried tests on either of my specimens to compare. (Sorry neither are in MinDat at present.) My Yerington piece is big enough that it's shed some smaller crystals in the package that I could sacrifice; not so much with the Northern Lights specimen. I can check it for cleavage.

Interesting question!

Cheers,

D.

16th Feb 2015 17:30 UTCDon Windeler

One tangential note I meant to include: I've never heard anything about from where in the Yerington district the cactus calcites were found. My guess is the big Yerington pit just because a lot of material was moved out of there and the appearance of the specimens falls within a time when it was still being mined. There are numerous mines and prospects in the district, however, leaving lots of other possible suspects.

Cheers,

D.

16th Feb 2015 17:50 UTCThomas Lühr Expert

"Replaced by calcite"....

The questioned specimen doesn't even looks like a pseudomorphosis, those are usually polycrystalline (there may be exceptions) and would be more milky. Also the most (or all ?) "aragonites" from this locality seem to be doubtful - in my opinion.

Of course, it's impossible to give a sure answer only by photos. More clearness we would have by a response of the owners of such specimens: Can they observe a perfect cleavage or not.

Thomas

PS: I'm not familar with american localities. But the confusion about aragonite/calcite is a frequent and worldwide problem.

16th Feb 2015 19:40 UTCJamison K. Brizendine 🌟 Expert

This may or may not be helpful to the discussion, but I have found one geological paper about Yerington, Nevada and its relationship with the Northern Lights Mine, that was published in Ophiolites, Arcs and Batholiths (Wright and Shervais 2008).

Although the paper doesn’t go into detail about the aragonite/calcite issue, it did provide two stratigraphic columns, one for Ludwig, Yerington District, Singatse Range, Nevada, USA and one for the Northern Lights Mine Area, Wassuk range, Mineral County, Nevada, USA (Proffett and Dilles 2008). As you can see the two stratigraphic columns are extremely similar.

I will keep you guys posted if I find anything else...

References Cited:

Proffett, J., and Dilles, J., 2008, Lower Mesozoic sedimentary and volcanic rocks of the Yerington region, Nevada, and their regional context, in Wright, J., and Shervais, J., eds., 2008, Ophiolites, Arcs, and Batholiths: A Tribute to Cliff Hopson: Geological Society of America Special Paper 438, p. 251-288.

17th Feb 2015 19:15 UTCReiner Mielke Expert

http://www.mindat.org/photo-666610.html and you know this is aragonite because?

17th Feb 2015 20:13 UTCUwe Kolitsch Manager

Message sent on 666610.

12th Feb 2016 16:15 UTCUwe Kolitsch Manager

Never got a reply on http://www.mindat.org/photo-666738.html - now changed.

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