had to look it up - I have some mica but is a clear crystal (often used instead of glass) - from images, looks like biotite mica.
RE: Blurtphoto: Agates, Amethyst and other strange rocks from Lake Superior Canada
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Blurtphoto: Agates, Amethyst and other strange rocks from Lake Superior Canada
https://www.minerals.net/mineral/biotite.aspx
Awesome … that’s it …
THE BIOTITE MINERAL GROUP
Biotite is a very common form of mica. It is named in honor Jean Baptiste Biot (1774 - 1862), a French physicist, mathematician, and astronomer who researched the mica minerals for their optical properties. Because of Biotite's abundance, its presence is usually lacking in collections except for it being an accessory mineral to other minerals. Biotite can come in enormous crystal sheets that can weigh several hundred pounds. Thin sheets can be peeled off as layers, and the thinner a layer is peeled the greater its transparency becomes.
In 1998, the IMA removed the status of Biotite as an individual mineral species, and instead declared it as a group name for the following individual members: Phlogopite, Annite, Siderophyllite, and Eastonite. However, mineral collectors still refer to Biotite by its traditional name and rarely make a distinction among its members except for Phlogopite.
Biotite is very hard to clean because if washed it will absorb water internally and start to break apart. The best way to wash Biotite and other Micas is with a dry electric toothbrush.
It’s used to make lamps … https://amzn.to/2UUvXAo
also used in things like microscopes and geiger-counters. lol. Glass is a horrible mess at the atomic level whereas a crystal has a nice structure that allows things like electrons to go through.