Well, somebody is getting somebody to mill and polish this shit. Probably not helpful except to perhaps show that there are indeed suppliers of this material out there....somewhere.
http://www.shoyeido.com/product/obsidian-4-inch/4-inch-round
But, looking around for stuff you will find other interesting factoids like this:
Synthetic glass ceramics had a serendipitous birth in Corning labs in the early 1950s. Research chemist Dr. Don Stookey was heating a piece of lithium disilicate glass that contained silver particles. The furnace was set to stop heating at 600° C. A malfunctioning thermostat let the temperature soar to 900° C. Instead of finding a pool of melted glass inside, though, Dr. Stookey found an opaque plate. It slipped out his tongs and fell to the floor, but didn’t shatter — leading to the development of CorningWare® cookware.
And this from Northrop Grumman...less than 10 angstroms is
REALLY smooth, right?.
CERAFORM Silicon Carbide can be directly polished to <10-Angstroms rms surface finish and with figures better than 1/10 PV. AOA Xinetics also uses the CERAFORM casting process for complex mechanical structures.
So, I'm of no help...but I did learn some things. LOL