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[Shifter55]

While working with some velvet obsidian I ran into some cutting issues: grinding with my 600 mesh lap caused these spherical delaminations to suddenly appear.

These weren't in the material to begin with, I'ld feel a slight change in friction and would be about 3/4 through cutting into one of these orbs despite there being no evidence of it below the surface of the stone.
I've heard of (and experienced )obsidian fracturing on saws due to internal strain but this is seems very different to that.
Has anyone else had this issue, and what can I do to prevent it?

[Felicia]

Don't know, small mineral bit present in the stone?? Never saw that before.

[Kaljaia]

Hm. that does seem odd, maybe a perlite crystobalite? I don't know if I'm spelling that correctly. A ball of spherical crystallization inside the glass that's only showing up once air or liquid gets into it?

[irockhound]

That was my best guess too.  I was thinking Crystobalite but the Spherule didn't make sense but I think you are right.

[Shifter55]

Hm. that does seem odd, maybe a perlite crystobalite? I don't know if I'm spelling that correctly. A ball of spherical crystallization inside the glass that's only showing up once air or liquid gets into it?

The shape and structure of christobalites seems to be a match, though these have a darker core that seems to be less porous!
Looking over the rough surface of this piece, I've found a pocket with a white residue that might be a worn-down christobalite, originally I though it was just a bubble with dirt washed in.