smoky quartz crystal cluster - teaching specimen from Novo Horizonte, Bahia, Brazil The oldest radiolarian fossils in

The oldest radiolarian fossils in the cherts lived about 200 million years ago

Asbestiform tremolite from the McIlroy Mine

These were printed over a period from 1907 to 1954

white gypsum sand from Lake Lucero

smoky quartz crystal cluster - teaching specimen from Novo Horizonte, Bahia, Brazil The oldest radiolarian fossils inTeaching smoky quartz cluster from Municpio Novo Horizonte, Bahia, Brazil. This area is famous for smoky quartz, often with rutile inclusions in the crystals. Smoky quartz forms from natural gamma radiation released by surrounding rocks. The radiation causes aluminum atoms, which replace silicon atoms in the crystal lattice, to transfer an electron to a neighboring positively charged ion, often Li+, forming an aluminum metal color center that darkens