Mica, variety "biotite"?, Silver Crater, near Bancroft, Ontario

"Biotite" was changed from a species name to a series name recently, so specimens like this are up in the air until mineralogists look at them further. Could be annite, lepidomelane, phlogopite, or a few others. Reminds one just how wiggly this supposedly straightforward science is!

This is a very nice specimen, large and showing all six sides, looking down on the cleavage face. Complete crystals can be quite interesting, tapering long hexagonal prisms, but the perfect cleavage ensures that they're seldom if ever collected intact. The Bancroft area was home to lots of mica mines, and produced some of the largest mica crystals in the world - measured in meters!

13 cm across, Photo copyright David K. Joyce