Browse Items (1651 total)

Sillimanite has been partly psuedomorphed

Macroscopic: Staurolite, garnet, biotite porphyroblastic, chlorite bearing, muscovite schist. Both garnets and staurolite are idiomorphic with the former highly poikiloblastic. The foliation in the schist bends around the porphyroblastic phases…

Hand Sample: Porphyritic rhyolite with medium-grained Potassium feldspar phenocrysts in a brown-red groundmass. Weathers to yellow-brown.

1:24000

1:24000

Mostly quartz, oligoclase, and microcline

1:24000

1:24000

Hand Sample: Holocrystalline, fine-grained phaneritic granite with crystals of potassium feldspar and smoky quartz. Weathers to orange-brown and light-gray.

Hand Sample: Hypocrystalline, porphyritic rhyolite. 20% subhedral to anhedral biotite, quartz, and microcline (sanidine) phenocrysts. 80% grey-brown groundmass. Massive.

1:62500

1:62500

A classic red-bed sample typical of the sandstones from the Supai Formation.

Both thin section images were taken at a 400x magnification.

Classic red-bed sample from the Supai Formation with silt-sized grains of mostly quartz. Some grains are semi-rounded.

Both thin section images were taken at a 400x magnification.

coarse grained