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They can have an average diameter 5–20 centimetres (2.0–7.9 in), [3] but can be much larger (for example, 300–370 centimetres (10–12 ft) at Silver Cliff in Colorado). Lithophysae are also related to the spherulites found in obsidians on the Italian island of Lipari , in Yellowstone National Park , and other places.
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.
Spherulites in rhyolitic ash, Hailstone Trail, Echo Canyon, Chiricahua Mountains, Arizona Spherulite markings on snowflake obsidian Photomicrograph of rhyolite, showing spherulitic texture (brown, between grey to white crystals) In petrology, spherulites (/ ˈ s f ɛr ʊ l aɪ t s, s f ɪər-/) are small, rounded bodies that commonly occur in ...
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 ...
Obsidian hydration dating (OHD) is a geochemical method of determining age in either absolute or relative terms of an artifact made of obsidian.. Obsidian is a volcanic glass that was used by prehistoric people as a raw material in the manufacture of stone tools such as projectile points, knives, or other cutting tools through knapping, or breaking off pieces in a controlled manner, such as ...
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Wilson Bentley micrograph showing two classes of snowflake, plate and column. Missing is an example of a needle. The shape of a snowflake is determined primarily by the temperature and humidity at which it is formed. [8] Freezing air down to −3 °C (27 °F) promotes planar crystals (thin and flat).
Cristobalite (/ k r ɪ ˈ s t oʊ b ə ˌ l aɪ t /) is a mineral polymorph of silica that is formed at very high temperatures. It has the same chemical formula as quartz, Si O 2, but a distinct crystal structure.