Geschichte: At ETHZ, I learned a lot about mineralogy. When I biked around in Alice Springs last January, I immediately recognised that a lot of pure minerals were laying around at the surface. I added a small hand specimen containing a 1/3 inch layer of pure biotite to my collection.
Geologie: The shining, greenish-grey and platy mineral is biotite which is part of a magmatic rock called pegmatite that often forms at shallow depths at temperatures of 400-500 °C. There, biotite and other minerals can grow big crystals. At the surface, biotite quickly loses its luster due to weathering. At the edge of the Simpson Desert rain is very rare, which helps to preserve the biotite.