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John Betts
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Location: New York City
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 Posted: Mar 27, 2020 15:42 Post subject: Rounded yellow-green crystals in calcite |
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I acquired an unlabeled specimen from a collection assembled around 1985-1995 that contained this specimen of translucent gray calcite with rounded yellow to yellow-green "blebs" of an unidentified mineral with an approximate hardness of <8>6.
The collector though he got it from Tanzania, but that cannot be counted on, given the time elapsed.
Any ideas that the yellow mineral might be?
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John Betts
Joined: 07 Jun 2012
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Location: New York City
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| Posted: Mar 27, 2020 15:43 Post subject: Re: Rounded yellow-green crystals in calcite |
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Another photo.
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Jordi Fabre
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| Posted: Mar 27, 2020 17:28 Post subject: Re: Rounded yellow-green crystals in calcite |
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Seems to be Prehnite on Calcite from Merelani
| Mineral: | Prehnite with Calcite |
| Locality: | | Merelani Hills, Lelatema Mountains, Simanjiro District, Manyara Region, Tanzania |  |
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| Dimensions: | Specimen size: 4.7 × 4.7 × 4.2 cm |
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Peter Megaw
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| Posted: Mar 27, 2020 19:12 Post subject: Re: Rounded yellow-green crystals in calcite |
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I was going to suggest a poorly formed calc silicate in a skarn. A needle will tell!
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Pete Richards
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| Posted: Mar 27, 2020 19:38 Post subject: Re: Rounded yellow-green crystals in calcite |
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I agree with Peter. Could even be a piece of a carbonatite. Suggestive somewhat of Crestmore, CA, or Oka, Quebec, or some places in upstate New York or the Grenville Province in Ontario/Quebec. Well-cooked limestone.
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John Betts
Joined: 07 Jun 2012
Posts: 207
Location: New York City
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| Posted: Mar 27, 2020 19:39 Post subject: Re: Rounded yellow-green crystals in calcite |
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| Jordi Fabre wrote: | | Seems to be Prehnite on Calcite from Merelani |
Thanks Jordi. That was actually my first thought, except there is no sign of bladed structure.
They look like the "melted" appearance found in spinel crystals from Mogok or Vietnam.
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John Betts
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Location: New York City
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| Posted: Mar 27, 2020 19:41 Post subject: Re: Rounded yellow-green crystals in calcite |
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I should have mentioned, there is no reaction to HCL which rules out most carbonates.
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Bob Carnein
Joined: 22 Aug 2013
Posts: 327
Location: Florissant, CO
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| Posted: Mar 28, 2020 10:37 Post subject: Re: Rounded yellow-green crystals in calcite |
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| The color looks right for Merelani prehnite, but the mode of occurrence and general appearance remind me of an iron-poor member of the humite series. I can't say I've ever seen a member of that series that's such a bright yellow color.
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lluis
Joined: 17 Nov 2006
Posts: 711
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| Posted: Mar 28, 2020 12:18 Post subject: Re: Rounded yellow-green crystals in calcite |
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Hi, all
As Bob said, it looks to me not as a prehnite from Merelani... When I saw it first, looked me more as a chondrodite or any related silicate. Yes,we all are thinking in silicates, but which one?...
An analysis would be magnificent!
Lluís
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