Sample SP118 - South White Peak

Alkali-feldspar microgranite porphyry

Click here for available geochemistry

Thin-section description

(South White Peak). Alkali-Feldspar microgranite porphyry. This rock is holocrystalline, porphyritic-aphanitic, with fine- to medium-grained subhedral crystals in a tan groundmass (27%) composed of feldspars, opaques, and fine-grained mica. All crystals are subhedral except the opaque minerals (<1 mm) which are subhedral to anhedral. Fluorite (<.1 mm) and quartz (.5 mm) are present as anhedral masses. The following are present as phenocryst phases: plagioclase and potassium feldspar (both .5-2 mm) are altered to fine-grained phyllosilicates and exhibit oscillatory zonation; hornblende (.5 mm) is rimmed by very fine-grained biotite; biotite (.2 mm) is altered to chlorite in places. The overall texture is granophyric. A mafic enclave (SP118e, Hornblende Diorite) is present (10 mm) comprised of subhedral crystals of: hornblende (3 mm); ferruginous biotite (1 mm); plagioclase (3 mm); potassium feldspar (3 mm); aegerine-augite (3 mm); zircon (<1 mm); apatite (<1 mm); opaques (<1 mm) are present as subhedral to anhedral crystals.