What a strange coincidence! My grandfather and his two sisters owned some perlite claims in central Arizona and my great aunt and uncle worked the claims for some years early in the 1900's. I remember my mother telling me about it and describing the rotary kiln that they used to cook the material into commercial perlite. It's basically degraded obsidian and it has some chemically bonded water in it. When it gets hot enough to melt the obsidian the water turns to super-heated steam and it puffs it up like popcorn. I can remember one of my great aunts mixing up cement and perlite and casting blocks from it. I think that she was trying to come up with a building material that had some insulating properties. It was all sold off sometime in the middle '60's. I still have a bunch of the Apache Tears from the mine around here somewhere. Funny I should focus on that. I don't think that I ever saw the raw material or the mine. Thank you for sorting that one out, Valeria.
J Marcus
http://flyrodjewelry.com/home.html