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Obsidian talus at Obsidian Dome, California Polished snowflake obsidian, formed through the inclusion of cristobalite crystals. The Natural History by the Roman writer Pliny the Elder includes a few sentences about a volcanic glass called obsidian (lapis obsidianus), discovered in Ethiopia by Obsidius, a Roman explorer.
Lithophysa. A lithophysa (plural lithophysae, from Greek lithos "stone" + physan "to blow") [ 1] is a felsic volcanic rock with a spherulitic structure and interior cavity with concentric chambers. Its outer shape is spherical or lenticular. They vary in size from very small up to twelve feet in diameter depending on the age of the magma ...
Spherulite. In petrology, spherulites (/ ˈsfɛrʊlaɪts, sfɪər -/) are small, rounded bodies that commonly occur in vitreous igneous rocks. They are often visible in specimens of obsidian, pitchstone, and rhyolite as globules about the size of millet seed or rice grain, with a duller luster than the surrounding glassy base of the rock, and ...
Apache tears are rounded pebbles of obsidian or "obsidianites" composed of black or dark-colored natural volcanic glass, usually of rhyolitic composition and bearing conchoidal fracture. Also known by the lithologic term marekanite, this variety of obsidian occurs as subrounded to subangular bodies up to about 2 in (51 mm) in diameter, often ...
Cristobalite spherulites formed by devitrification from the obsidian matrix. Specimen from California, US; size: 5.9 cm × 3.8 cm × 3.8 cm (2.3 in × 1.5 in × 1.5 in). Cristobalite (/ krɪˈstoʊbəˌlaɪt /) is a mineral polymorph of silica that is formed at very high temperatures. It has the same chemical formula as quartz, SiO 2, but a ...
Snowflake obsidian after tumble polishing. The precise tumbling duration is determined by many factors, including the hardness of the rock and the degree of smoothing desired in the coarser steps. Some people will tumble stones with rough grit for two, three or even four weeks to get their desired shapes out of the stones.
Snowflake. A snowflake is a single ice crystal that has achieved a sufficient size, and may have amalgamated with others, which falls through the Earth's atmosphere as snow. [1][2][3] Each flake nucleates around a tiny particle in supersaturated air masses by attracting supercooled cloud water droplets, which freeze and accrete in crystal form.
Porphyry (geology) Porphyry (/ ˈpɔːrfəri / POR-fə-ree) is any of various granites or igneous rocks with coarse-grained crystals such as feldspar or quartz dispersed in a fine-grained silicate -rich, generally aphanitic matrix or groundmass. In its non-geologic, traditional use, the term porphyry usually refers to the purple-red form of ...