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Magma rich in silica and poor in dissolved water is most easily cooled rapidly enough to form volcanic glass. As a result, rhyolite magmas, which are high in silica, can produce tephra composed entirely of volcanic glass and may also form glassy lava flows. [2] Ash-flow tuffs typically consist of countless microscopic shards of volcanic glass. [3]
Obsidian (/ ə b ˈ s ɪ d i. ən, ɒ b-/ əb-SID-ee-ən ob-) [5] is a naturally occurring volcanic glass formed when lava extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock . [ 6 ]
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 ...
1 Japan: 1991 [39] 40 Dieng Volcanic Complex: 2 Indonesia: 1928 [30] 39 Taal: 4 Philippines: 2020 2020–2022 Taal Volcano eruptions: 38 Dieng Volcanic Complex: 2 Indonesia: 1786 [30] 32 Mount Nyiragongo: 1 Democratic Republic of the Congo: 2021 2021 Mount Nyiragongo eruption: 32 Kelud: 4 Indonesia: 1990 [40] 31 Bayonnaise Rocks: 2 Japan: 1952 ...
The alkaline magmas of volcanic ocean islands will very occasionally differentiate all the way to peralkaline rhyolites, but differentiation usually ends with trachyte. [25] Small volumes of rhyolite are sometimes erupted in association with flood basalts, late in their history and where central volcanic complexes develop. [26]
Obsidian projectile point.. Obsidian is a naturally formed volcanic glass that was an important part of the material culture of Pre-Columbian Mesoamerica.Obsidian was a highly integrated part of daily and ritual life, and its widespread and varied use may be a significant contributor to Mesoamerica's lack of metallurgy.
Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-grained to aphanitic chilled margins which may contain tachylite (dark mafic glass). Diabase is the preferred name in North America, while dolerite is the preferred name in the rest of the English-speaking world, where sometimes the name diabase refers to ...
Glass is abundant in the Lunar regolith and forms as a result of impact melting. Ice is an important mineral in permanently shaded craters. [ 12 ] Lunar regolith is divided into highland and mare on the basis of their composition, and further divided into high-, low-, and very low-titanium on the basis of their ilmenite content.