FMF - Friends of Minerals Forum, discussion and message board

[rhichens]

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.

[Dale Hallmark]

Looks like garnets to me.
Dale

[monicaiRocks]

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

[kushmeja]

[Bob Harman]

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

[John S. White]

Almost certainly garnet. How sure are you about the locality?

[marco campos-venuti]

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.

[rhichens]

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.

[Michael Shaw]

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.

[kushmeja]

[rhichens]

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.

[rhichens]

[Bob Harman]

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

[Jordi Fabre]

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

[rhichens]

Thanks all.