FMF - Friends of Minerals Forum, discussion and message board

[LoveAlwaysBlake]

Hi everyone.

My husband works at an underground coal mine in Southern Indiana and always brings me neat things home. There was a fall last week and he brought me home my first (like 50 pcs) of what I assume is just quartz? I want to be sure there's nothing too rare or special about these before i try to clean and cut into it. Im a beginner.. like this will be the 2nd time I try to cut. He keeps telling me how old it is and its making me super nervous (but I'm more excited to mess with it honestly). Any help appreciated! Thanks everyone.

[Pete Richards]

Is this one thing or two things? The brownish stuff - is it attached to the white stuff behind it?

From your photo, I would say that the brown stuff is pyrite - fool's gold - an iron sulfide. The white stuff behind it appears to be quartz.

There is nothing of great value here, so if you want to try cutting it, go ahead and have fun.

If I am right about the brown stuff being pyrite, it will probably color the cutting water black as you cut it. Both it and the quartz are brittle, so fracturing is quite possible. Watch out for glass-sharp shards from the quartz.

[Bob Carnein]

This appears to be calcite, but there are both white parts and brown parts in your photo. You can do several things to test it. Break a piece off and see whether it breaks into diamond-shaped pieces, sort of "squashed cubes" (your photo looks like it will). Second, heat some vinegar and crush a bit of the sample. Dump it into the vinegar, and, if it's calcite, it will "fizz". Third, try the hardness with a pocket knife. Calcite is a lot softer than steel.

[LoveAlwaysBlake]

pic 2

[LoveAlwaysBlake]

Sorry I was trying to attach the other pics. This is 4 or 5 pieces yes!

[LoveAlwaysBlake]

[LoveAlwaysBlake]

[Bob Harman]

I would like to set the identification record straight for what you are showing.

For the record, I have collected Indiana minerals for 40 years and I live in Bloomington, IN. My wife's whole family is from SW Indiana, near Princeton, so we are abundantly familiar with the coal mining industry where you live.

The whitish mineral that you have is calcite. It is abundant, as seams, in the sedimentary limestone and shale near to the coal seams. Other than in geodes in south central Indiana, there is no quartz down there in SW Indiana including in the coal mines. Calcite is your whitish mineral.

The brown colored "mineral" looks much more like calcite covered by a very thin layer of dried oil.......bitumen. If you break a piece, the fresh break will look white like the calcite you show. Look closely at the last photo above. In the chipped areas, you can see where the brown color is just a thin coating rather than a discreet crystal-like mass.
Bitumen is dried oil.......remember that there are oil wells near to you in SW Indiana as well. Bitumen covers the surface of lot of the rock, including calcite, facing fissures and small cavities. Occasional small deposits of oil are commonly found in the limestone cavities in southern Illinois and coal mining areas of SW Indiana. BOB