On 04/11/2016 01:15, whit3rd wrote:
On Thursday, November 3, 2016 at 9:41:15 AM UTC-7, N_Cook wrote:
Anyone ever seen this before? Basically clear mica but with black smokey
looking intrusions, something geological in the way of tar/bitumen
leeching into the cleaving planes?

Sure; Amelia County, VA has some old mica mines, the native stuff is near black
(but that's 0.3 inch thick, and it's prepared by cleaving down to 0.003"
thickness).


I don't suppose you happen to know whether the insulation property is
just the same? I'm thinking whether the black material may absorb water
vapour