FMF - Friends of Minerals Forum, discussion and message board

[Hardman.digs]

So is this a common occurrence anywhere? It's the first time I have run into this sort of thing in Oregon. Its an opalized scoria that's for sure. Also I'm wondering how bad of an idea it would be to try to slice up some for small interesting cabochons. The overall size of the piece is about 3 x 4 x 7 inches.

[marco campos-venuti]

Scorias are often filled by silica because cavities drain water. It is difficult to find empty cavities in old scorias from the geological record. More often they are filled by something, zeolites, carbonates or silica. Some vesicular basalts contain precious opal and others are filled by small agates. I guess you can polish, both opal and scoria glass take a good polish and have similar hardness.
Enjoy cutting!!