Browse Items (32 total)

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

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

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 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 medium-grained phaneritic granite with crystals including potassium feldspar and smokey quartz.

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

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

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

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

Hand Sample: Porphyritic diabase with coarse to very coarse grained subhedral pink-green plagioclase laths approximately 3cm in length set in a gray-black matrix. Inclusions of matrix present within plagioclase laths. Weathers to orange-brown.

Hand Sample: Aphanitic, grayish-white with some patches of fine-grained grey crystals. Weathers to medium yellow-brown.

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

Hand Sample: Phaneritic rhyolite with fine-grained phenocrysts of quarts, feldspar and hornblende in a brownish-red groundmass. Weathers to orange-brown.

Hand Sample: Aphanitic grey-black color. Weathers to yellow-tan and orange. Small vesicles present.

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

Hand Sample: Porphyritic (or coarse-grained phaneritic) diorite with coarse-grained white plagioclase laths up to 1cm and some black mineral. Weathering to rust-orange color.

Hand Sample: Porphyritic orange-pink rhyolite. Dominantly potassium feldspar with some black crystals. Weathers to brown-black and yellow-brown.

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