Browse Items (32 total)

Hand Sample: Holocrystalline, coarse-grained, phaneritic granite with dominant alkali feldspar crystals, as well as quartz and plagioclase feldspar. Veins or pockets of dark brown-black material dispersed intermittently.

Hand Sample: Holocrystalline phaneritic, porphyritic and granophyrite rich in alkali feldspar. Larger crystals or pockets of biotite and quartz also present. Rock is weathered to orange brown. Contact on one side with dark black-brown quartz-rich…

Hand Sample: Holocrystalline fine-to-medium-grained phaneritic rhyolite with quartz, biotite, and plagioclase crystals generally no larger than 2mm. Weathers to brownish-orange.

Hand Sample: Porphyritic rhyolite with medium-grained potassium feldspar and plagioclase feldspar phenocrysts in a dark red-brown matrix. Weathers with an orangish tinge.

Hand Sample: Porphyritic medium-grained phenocrysts of potassium feldspar in a dark purple-red groundmass. Weathers to white and orange-brown.

Hand Sample: Holocrystalline, fine-to-medium-grained granite. Mineralogy includes potassium feldspar and quartz. One corner of rock has a mass of dark grey-brown groundmass with inclusions of plagioclase laths and anhedral grey-green crystals.…

Hand Sample: Porphyritic diabase with light crystals in a dark-grey-to-black groundmass. Plagioclase 45%, Pyroxene 45%, Hornblende 5%, Olivine and Biotite 5%

OCR PDF of supplemental information for the St. Francois Mountains collection.

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

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.

Hand Sample: Fine-grained phaneritic granite. Mineralogy includes potassium feldspar, quartz and a black mineral. Weathers to light orange.