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Is this Calcite or Dolomite
  
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xdxucn




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PostPosted: Jul 29, 2020 23:26    Post subject: Is this Calcite or Dolomite  

I've got a piece of specimen, which said to be Galena+Calcite from Russia.

In Rock and Gem magazine, April 2017, there's an article "Is it Calcite or Dolomite". In the article, it says that it is Dolomite not Calcite. I'm confused. Any one could give me a clear answer? Thanks

Xiao-dong



06.JPG
 Mineral: Galena
 Locality:
Dalnegorsk, Dalnegorsk Urban District, Primorsky Krai, Russia
 Description:
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Matt_Zukowski
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PostPosted: Jul 30, 2020 03:34    Post subject: Re: Is this Calcite or Dolomite  

Are you talking about the August 27, 2019 article, with a picture at the bottom that looks like your specimen? The caption in this article says that that specimen came from a "borate mine in far-east Siberia."
https://www.rockngem.com/is-it-calcite-or-dolomite/

The borate mines in far-east Siberia are in Dalnegorsk, and this search for dolomite in the Dalnegorsk region shows specimens that look like yours, especially from the 2nd Sovetskii Mine.
https://www.mindat.org/gallery.php?loc=2635&min=1304

BTW - that is a beautiful specimen.
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John Betts




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PostPosted: Jul 30, 2020 09:36    Post subject: Re: Is this Calcite or Dolomite  

A simple hardness test will distinguish between calcite and dolomite Can you scratch the crystals on your specimen with a calcite crystal? Do your crystals scratch calcite?
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vic rzonca




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PostPosted: Jul 31, 2020 07:10    Post subject: Re: Is this Calcite or Dolomite  

Both are carbonates. Calcite is calcium carbonate, dolomite is calcium magnesium carbonate. I'm not sure I've answered the question you've asked.
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Jesse Fisher




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PostPosted: Jul 31, 2020 10:46    Post subject: Re: Is this Calcite or Dolomite  

As Vic mentioned, calcite is calcium carbonate, and dolomite is calcium, magnesium carbonate. Some sort of chemical test for magnesium would distinguish them, but would cost a bit. Physically, calcite is softer than dolomite. Calcite has a hardness of 2.5 - 3, where-as dolomite is 3.5 - 4. Dolomite will scratch calcite, but not the reverse. Also, dolomite is less soluble in cold acids (such as HCl) than calcite. If a bit of it fizzes readily in acid, it is likely calcite, if slowly then dolomite is likely.
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Bob Harman




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PostPosted: Jul 31, 2020 11:40    Post subject: Re: Is this Calcite or Dolomite  

I find the responses to this poster's question.....showing off his specimen.....interesting.

The only really spot on statement was Matt Z's comment: "BTW, that is a beautiful specimen".

John B's suggestion to 'scratch the crystals' to help identify the mineral seems to me to be dangerous. There is a high likelyhood that attempting that, might just knock a crystal off, and even just scratching one damages "the beautiful specimen". For this particular specimen, do not(!) attempt what John B suggests.

What Jesse F suggests might be true, but for this particular small size "beautiful specimen" finding a safe area to put acid on the crystals for testing is just as unappealing to me.
[There is just no area that allows acid testing without being visible.]

For this particular hi quality specimen with small and rather delicate calcite/dolomite crystals delicately attached to the galena, do not attempt anything that just might ruin or damage your example.

To resolve the basic mineral identification question, I would review other similar examples from this locality; some should have the mineral ID known. My opinion, Bob
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John Betts




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PostPosted: Jul 31, 2020 20:52    Post subject: Re: Is this Calcite or Dolomite  

Just determine the hardness. It is not rocket science. If you are willing to perform basic tests, then why post to this forum.
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xdxucn




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PostPosted: Jul 31, 2020 22:42    Post subject: Re: Is this Calcite or Dolomite  

Thanks for the answer. Maybe I can do a little hardness test on the back corner side of the specimen. And I will let you know the result.

As for identification of similar samples, some says it's calcite, some says it's ferroan calcite, in the Rock&Gem magazine, it says it's dolomite, and the label coming with the specimen says it's calcite. Maybe I should identify it myself sometime later. :)
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Matt_Zukowski
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PostPosted: Aug 01, 2020 01:52    Post subject: Re: Is this Calcite or Dolomite  

The fizz test is also useful, and can be done on a very small area of the sample, so don't forget about that.

Another thing to look for are saddle-shaped xtals or aggregates of xtals. Dolomite sometimes shows pronounced curved xtal faces. I don't see any curved xtal faces in the picture, and that doesn't rule out dolomite, but maybe there are some curved faces you can see, which would suggest it is.

Frankly, based on the pictures in the R&G article and those from mindat, I'd feel comfortable calling it dolomite. But i also wouldn't be above doing hardness and fizz testing.
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