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Link Posted: 3/15/2009 11:04:43 AM EDT
Originally Posted By Windustsearch:
Originally Posted By SRM:
Looks a little translucent for goethite and while iron-rich sphalerite (marmatite) can be that color, it is uncommon at best.

But I could be wrong.

SRM


It isn't remotely close to translucent.

I have found both minerals in the presence of a geologist and both looked similar to the OPs specimen- the geothite was a little lighter in color, more similar to lead.



Let's call it a professional disagreement then, shall we? Below are three examples of sphalerite, one from several years ago, one from a few months ago and one from Monday. The one on the left is derived from magmatic sources (according to the sulfur isotopes), while the two on the right are from sedimentary sources. These are all carbonate hosted,though the first has undergone complete replacement during paragenesis. The OP's rock shows what appears to be sulfide minerals. While sulfides and oxides can exist in the same rock, especially near the surface, one typically sees a greater degradation of sulfides and iron staining.

Like I said, I could be wrong


SRM

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