Browse Items (32 total)

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

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

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

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

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

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

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

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

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, 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: Phaneritic granite with coarse-grained phenocrysts of smokey quartz and generally smaller crystals including potassium feldspar. Weathers to orange on one side and some light-gray material on the other.

Hand Sample: Porphyritic latite with medium-to-coarse-grained subhedral plagioclase phenocrysts in a brown-black groundmass. Thin black veins present with green margin of contact on either side.

Hand Sample: Holocrystalline, phaneritic, fine-to-medium-grained quartz monzonite. Mineralogy includes large plagioclase laths up to 8mm in length, quartz, alkali feldspar, biotite. Very large crystals of a dark material up to 3cm in length.…

Hand Sample: Phaneritic rhyolite. 10% fine-grained phenocrysts of sanidine and quartz and 90% dark-brownish-red groundmass. Weathers to brown-orange.

Hand Sample: Holocrystalline medium-grained phaneritic granite with crystals including potassium feldspar and smokey quartz.

Hand Sample: Aphanitic, pyroclastic grey-black tuff. Conchoidal fracture pattern from a strike-point on one edge. Weathers to yellow-brown.

Hand Sample: Porphyritic fine-grained light-pink and black phenocrysts in a reddish-purple-brown matrix. Hospitable to grey-brown lichen.

Hand Sample: Holocrystalline, medium-grained phaneritic granite with smoky quartz, potassium feldspar, and biotite