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Need help identifying this rock

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This black rock was found in the central Philippines in an island called Negros Occidental. The guy who found it said he had never seen a rock like it before and thought it to be rare. He conducted tests on the strength of the rock by hammering it and striking it with a pickaxe to see if it would break. He said it was extremely hard but he was able to split a portion of the rock. You can also see dents on the surface from where the pickaxe made contact. The shard that broke off was used to cut glass and apparently it worked.

I'd appreciate any help you can offer in regard to identifying this thing, as you can tell I know almost nothing about rocks but I thought I'd ask here to help this guy out. He seems convinced that this rock has great value. My guess is that it's some sort of igneous rock due to the volcanic nature of the Philippines.

asked Sep 18, 2014 by RicBenz (120 points)

2 Answers

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I would say diamond, black diamond, although it could be obsidian. If it cuts glass, it could be a diamond. The only thing which makes me think differently is the pitting, maybe caused by softer materials embedded in the obsidian being eroded away.

answered Sep 18, 2014 by Weasel (32,730 points)
0 votes

Highly unlikely to be diamond due to its rarity and limited occurences. The conchoidal fracture is a strong indicator of obsidian. Several questions I would ask to further be able to identify it:

1) Is this from a volcanic zone? Are there others in the area? 2) Any way to test its hardness? Or perhaps even try to scratch quartz with it to see if it scratches. 3) Any way to post additional photos of better quality?

answered Sep 19, 2014 by hershel (45,560 points)

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