Found Object: A Mysterious Black Stone

2 scans of the same black beach stone - 2013, DS

(click to enlarge)

I actually found two stones on the coastline today, made of the same mineral... but, the one shown is the most photogenic, and this is it's best side... scanned at 200%, and then blown-up another 200%. For the top one, I used the "light adaption" scanning feature, but, both scans exhibit the same peculiar chromatic artifacts that are created when a glassy object is scanned: there's a distinct polarization of red and blue which is impossible to modify... but, in this case, actually enhances the image.

I've no idea what sort of mineral it is. Some surface areas are glassy, but, the rougher areas have zillions of tiny flecks of what is probably silica, and which reflect a rainbow of colors...

In any case, it's a keeper! :-)

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The other volcanic rock - 2013, DS
(click to enlarge)

Update (6/30):  My friend, Moo, has just informed me, that yesterday's found objects are bits of volcanic rock known as rainbow obsidian. (Thanks, Moo!)

I've googled it, and, while it surely is an igneous rock, I'm not sure it's wholly obsidian - certainly not gem quality - and might be the combination of basalt and obsidian known as a tachylite.

In any case, it's pretty cool to have some volcanic rock, and it's really quite handsome, (though not in the bismuth crystal league). Also, it probably has bits of plagioclase feldspar, and, if you remember, that's the family labradorite belongs to.

Judging by the lack of saltwater erosion, my specimens may have originated from one of the more recent volcanic eruptions... though, how they arrived on a Connecticut shoreline is, yet, another mystery... but, you can bet I'll be looking for more! (For the sequel to this story, see: Obsidian Glass (& a "moon rock").

(Note: obsidian is an anagram of my name...)