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Please help identify this mineral/crystal.
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rhichens




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PostPosted: Aug 29, 2016 13:03    Post subject: Please help identify this mineral/crystal.  

Any help with identifying this mineral would be much appreciated. The whole specimen has a lovely sparkle that unfortunately doesn't show up in the photos. The surface in many places has a silver, almost glassy appearance. Some areas have a white or light grey powdery appearance. There are clusters of dark red crystals and areas of metallic, black crystals that may be galena.


DSCN3326 (2).JPG
 Mineral: Unknown
 Locality:
Cornwall, England, United Kingdom
 Dimensions: 8cm x 5.5cm x 4.5cm
 Description:
 Viewed:  3750 Time(s)

DSCN3326 (2).JPG


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Dale Hallmark




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PostPosted: Aug 29, 2016 13:13    Post subject: Re: Please help identify this mineral/crystal.  

Looks like garnets to me.
Dale
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monicaiRocks




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PostPosted: Aug 29, 2016 13:23    Post subject: Re: Please help identify this mineral/crystal.  

If from Cornwall, more likely to be Sphalerite than garnets I think, right?
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kushmeja




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PostPosted: Aug 29, 2016 13:35    Post subject: Re: Please help identify this mineral/crystal.  

monicaiRocks wrote:
If from Cornwall, more likely to be Sphalerite than garnets I think, right?


I was thinking sphalerite myself, as that's usually found associated with galena. If it's truly from Cornwall, there's both sphalerite and garnets (almandine, spessartine) found there.
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Bob Harman




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PostPosted: Aug 29, 2016 13:51    Post subject: Re: Please help identify this mineral/crystal.  

While I am not that familiar with Cornwall minerals and their combinations, similar appearing small sphalerite crystals on massive sphalerite (called ruby jack) are found in many areas of the US Midwest. In fact, I do not see definite evidence of galena. Here in the Midwest massive sphalerite, when cleaved, has a silvery sheen that novice collectors often mistakenly misidentify as galena. I too favor sphalerite.....perhaps all sphalerite. BOB
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John S. White
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PostPosted: Aug 29, 2016 14:17    Post subject: Re: Please help identify this mineral/crystal.  

Almost certainly garnet. How sure are you about the locality?
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marco campos-venuti




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PostPosted: Aug 29, 2016 14:49    Post subject: Re: Please help identify this mineral/crystal.  

In the upper portion there is an other mica family mineral resembling Clinochlore (Var: Pennine).
Isn't it?
In this case it could be a garnet from a Rodingite vein.
And in this case it would be more likely from western Italian alps.
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rhichens




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PostPosted: Aug 29, 2016 15:05    Post subject: Re: Please help identify this mineral/crystal.  

Thank you all for your comments! I'm not sure at all of the origin of this specimen. I live in Cornwall and acquired it from someone in Cornwall (now deceased so I can't ask about origins) but that's all I know. Here's another photo showing what appears to be galena.


DSCN3309.JPG
 Dimensions: 8
 Description:
 Viewed:  3638 Time(s)

DSCN3309.JPG


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crosstimber
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PostPosted: Aug 29, 2016 15:11    Post subject: Re: Please help identify this mineral/crystal.  

Some have suggested garnet while others think it is sphalerite. This serves to illustrate how difficult it is to identify a specimen with only a picture and no tests.

A simple test that you can do to eliminate one of these suggested identifications is a hardness test. Sphalerite is relatively soft with a hardness of 3.5-4.0. The hardness of garnet, on the other hand, is 6-7.5. A simple scratch test will reveal the approximate harness of the mineral you are trying to identify. A steel knife has a hardness of about 5, so scratch the specimen, and if the knife does not leave a scratch, the hardness of the mineral is more than 5. This will eliminate sphalerite.
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kushmeja




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PostPosted: Aug 29, 2016 15:17    Post subject: Re: Please help identify this mineral/crystal.  

rhichens wrote:
Thank you all for your comments! I'm not sure at all of the origin of this specimen. I live in Cornwall and acquired it from someone in Cornwall (now deceased so I can't ask about origins) but that's all I know. Here's another photo showing what appears to be galena.


I see nothing in this photo that looks similar to galena. Galena is a metallic mineral and would be opaque and metallic, whereas these crystals appear to be dark red and translucent.
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rhichens




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PostPosted: Aug 29, 2016 15:23    Post subject: Re: Please help identify this mineral/crystal.  

The dark mass of crystal near the top of the specimen in the photo is indeed metallic and shiny just like specimens of galena that I have.
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rhichens




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PostPosted: Aug 29, 2016 15:32    Post subject: Re: Please help identify this mineral/crystal.  

crosstimber wrote:
Some have suggested garnet while others think it is sphalerite. This serves to illustrate how difficult it is to identify a specimen with only a picture and no tests.

A simple test that you can do to eliminate one of these suggested identifications is a hardness test. Sphalerite is relatively soft with a hardness of 3.5-4.0. The hardness of garnet, on the other hand, is 6-7.5. A simple scratch test will reveal the approximate harness of the mineral you are trying to identify. A steel knife has a hardness of about 5, so scratch the specimen, and if the knife does not leave a scratch, the hardness of the mineral is more than 5. This will eliminate sphalerite.


Thank you for this helpful suggestion. I just tried the test and the specimen did scratch (both the red crystal and the shiny base mineral). So not garnet but possibly sphalerite!
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Bob Harman




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PostPosted: Aug 29, 2016 15:38    Post subject: Re: Please help identify this mineral/crystal.  

Like I said before, there is nothing in your newest photo that looks like galena. Cleaved and broken surfaces of sphalerite can easily be misidentified. It still looks like sphalerite to me, especially the crystal surfaces at the top area of your newest picture. Garnet (from Cornwall or other locales) seems a possibility (especially to others) as well. Because there is a difference of opinion, worthwhile to do some testing and show it around, in person, at a local club meeting or college geology department. BOB
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Jordi Fabre
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PostPosted: Aug 29, 2016 17:36    Post subject: Re: Please help identify this mineral/crystal.  

Sorry to disagree with John but nothing seems point to Garnet and everything seems to point to Sphalerite...
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rhichens




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PostPosted: Aug 29, 2016 18:26    Post subject: Re: Please help identify this mineral/crystal.  

Thanks all.
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CranCowan




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PostPosted: Sep 28, 2016 23:25    Post subject: Re: Please help identify this mineral/crystal.  

Sphalerite will dissolve in muriatic acid (HCl). It produces H2S gas which smells like rotten eggs.
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Bob Harman




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PostPosted: Sep 29, 2016 07:45    Post subject: Re: Please help identify this mineral/crystal.  

Sphalerite is a sulfide.....ZnS..... I thought CARBONATES dissolved in some acids such as muriatic acid (28% HCl). I never had a sphalerite show evidence of dissolving when I cleaned it.
Am I now right or wrong? BOB
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geofossile




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PostPosted: Sep 29, 2016 07:59    Post subject: Re: Please help identify this mineral/crystal.  

rhichens wrote:
Any help with identifying this mineral would be much appreciated. The whole specimen has a lovely sparkle that unfortunately doesn't show up in the photos. The surface in many places has a silver, almost glassy appearance. Some areas have a white or light grey powdery appearance. There are clusters of dark red crystals and areas of metallic, black crystals that may be galena.


I think it is sphalerite.
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CranCowan




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PostPosted: Sep 29, 2016 08:05    Post subject: Re: Please help identify this mineral/crystal.  

Bob Harman wrote:
Sphalerite is a sulfide.....ZnS..... I thought CARBONATES dissolved in some acids such as muriatic acid (28% HCl). I never had a sphalerite show evidence of dissolving when I cleaned it.
Am I now right or wrong? BOB


True, carbonates dissolve in HCl but so does ZnS (try it and see). The products are zinc chloride and hydrogen sulfide). It won't fizz like calcite but it should produce a stinky smell.
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PostPosted: Nov 25, 2016 10:43    Post subject: Re: Please help identify this mineral/crystal.  

The textbooks (Dana's System) confirm that sphalerite is soluble in hydrochloric acid with the evolution of hydrogen sulfide. This reaction may be a little bit slow for easy detection, but would be sped up with the use of warm hydrochloric acid applied to a powdered mineral sample. It might even fizz slightly, since hydrogen sulfide is a gas.

A further distinction is that sphalerite has very good cleavage in several directions, while garnet lacks cleavage, though it sometimes may show parting that can be mistaken for cleavage.

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