#schist

"Gneissoid contorted schist." Rocks and Rock Minerals. 1908.

Sculpture (schist) of the seated Buddha, made in the 2nd or 3rd century CE by an artist active in present-day Pakistan, then part of the Kushan Empire. The sculpture is representative of the Gandhara style, also known as Greco-Buddhist, which resulted from the fusion of Hellenistic Greek influences brought eastward by Alexander the Great's conquests with native artistic traditions of central and southern Asia.

Zebra Schist outcrop, Kangaroo Island, South Australia.

Gandharan head of a Buddha (grey schist, 3rd-4th century AD)

This week's Member Box spotlight: Almandine Garnet -- the deep-red garnet most people picture when they hear "garnet.Fe3Al2(SiO4)3, a magnesium-free iron end-member of the pyralspite garnet series.This raw cluster comes from a schist host rock in Fujian Province, China. The crystals form classic rhombic dodecahedra (12- Chemical formula faced), sometimes modified by trapezohedra (24 faces) -- the most recognizable geometry in the mineral kingdom.

Member Box notes:

Formed under high pressure and temperature in metamorphic rock

- Mohs hardness 7.5 -- tough enough for industrial abrasive (sandpaper garnet!)

- Red color comes from ferrous iron substituting into the octahedral sites

- Distinguishes between almandine vs pyrope vs spessartine by exact iron/aluminum balance

- A classic starter stone for crystal system studies -- isometric, perfect symmetry

Fun geology fact: garnet-bearing schist is a pressure-temperature indicator. If you find crystals like these in the field, you know you're standing on rocks that were once buried 10 to 30 km deep. That's how old, dense collisional mountain belts become accessible at the surface.

Oh, schist! Another metamorphic petrology practical class.