well, I'm not sure but that sounds similar to the kind of sand used in the rock tumblers..
don't quote me on it but it's something like that.
google would confirm or say otherwise.

DH uses "his" tumbler to shine up his brass bullet casings .... he uses ground Walnut Shells or ground up corn cobs . That's alot more coarse than this sand.

Notice I said " HIS " .... maybe I Can get him to share ~~ LOL

TMG,
Seaglassic shared this web site:
www.artofmosaic.com in another thread.
On one page (the link is below) I saw these wall plaques... concrete I guess... with the open areas. Can't help but wonder what your black Silica would look like inside this kind of openings. Or maybe dusted over grout... on something that wouldn't be touched? It's kind of shiny, right?

Here is a link that might be useful: Interesting stuff

Saw this one day on tv and thought this application using polymer clay could be very awesome along with a glass mosaic. I think you could adapt it for other things. Not sure about silica in the oven though.

Here is a link that might be useful: sand and polymer clay

Hmmmmm...
I know! Ya got any CATS????