obsidian

ALASKA VOLCANO OBSERVATORY GLOSSARY
A black or dark-colored volcanic glass, usually composed of rhyolite.
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USGS PHOTO GLOSSARY OF VOLCANIC TERMS
Obsidian is dense volcanic glass, usually rhyolite in composition and typically black in color. Compared with window glass, obsidian is rich in iron and magnesium; tiny (0.005 mm) crystals of iron oxide within the glass cause its dark color.
Obsidian is often formed in rhyolite lava flows where the lava cools so fast that crystals do not have time to grow. Glass, unlike crystals, has no regular structure and therefore fractures in smooth conchoidal (curved) shapes. The intersections of these fractures can form edges sharper than the finest steel blades. For this reason, obsidian was used by many native cultures to make arrowheads and blades.
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More about color of obsidian
The colors in obsidian result from the oxidation state of the chemical elements within the tiny minerals that are finely dispersed in the glass. Black color results chiefly from magnetite, Fe304. If the obsidian is highly oxidized, then the glass may contain hematite, which provides a reddish hue. Variations in the oxidation state of the iron (Fe) varieties imparts a slight greenish hue. Some obsidian is banded, a consequence of oxidation on a flow surface being folded into the lava as it continues to move.

Glossary of volcanic terms. - University of Wisconsin Oshkosh. . 2001.

Look at other dictionaries:

  • Obsidian — (glänzend), Bims (mattgrau im Vordergrund) und Rhyolit (heller, rechts) …   Deutsch Wikipedia

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  • obsidian — OBSIDIÁN, obsidiane, s.n. Rocă vulcanică de culoare neagră sau brună cenuşie, cu înfăţişarea sticlei topite, care a fost folosită în epoca de piatră pentru confecţionarea armelor şi a uneltelor. [pr.: di an] – Din fr. obsidiane, obsidienne, lat.… …   Dicționar Român

  • Obsidian — est un jeu de rôle édité en français par 7e cercle. Il mêle habillement les genres, allant du cyberpunk au post apocalyptique en passant par l occulte. Obsidian va mener les joueurs dans un univers sombre et violent, où l humanité se cache dans… …   Wikipédia en Français

  • obsidian — ob*sid i*an, n. [L. Obsidianus lapis, so named, according to Pliny, after one Obsidius, who discovered it in Ethiopia: cf. F. obsidiane, obsidienne. The later editions of Pliny read Obsianus lapis, and Obsius, instead of Obsidianus lapis, and… …   The Collaborative International Dictionary of English

  • Obsidian — (Obsidianus lapis [weil Obsidius ihn zuerstin Äthiopien gefunden haben soll], auch Hahnstein, Glasachat, Glaslava, Glaszeolith), Mineral, erscheint amorphisch in derben, dichten Massen, in Kugeln, rundlichen Körnern u. Geröllen, porös, selten… …   Pierer's Universal-Lexikon

  • Obsidĭan — (Glaslava, Lavaglas), die wasserfreie oder nur bis 2 Proz. Wasser enthaltende glasartige Modifikation der Trachyte, meist schwarz (schwarze Glaslava) und grau, auch gelb, braun, rot, grün, selten blau, stark glasglänzend, durchsichtig bis… …   Meyers Großes Konversations-Lexikon

  • Obsidian — Obsidian, s. Gläser, natürliche …   Lexikon der gesamten Technik

  • Obsidian — Obsidiān, natürliches, vulkanisches Glas, durch rasche Abkühlung bes. kieselsäurereicher Schmelzmassen entstanden, samtschwarz oder braun, selten grau oder grün, von der chem. Zusammensetzung der Rhyolithe und Trachyte, bildet für sich Ströme,… …   Kleines Konversations-Lexikon

  • Obsidian — Obsidian, Pseudochrysolith, Fluolith, in Kugeln oder Körnern (Marekanit) vorkommendes glasartiges Mineral, von 2, 3 spec. Gewicht, von grauer, gelber, rother, brauner, meistens aber schwarzer Farbe, selten farblos u. beinahe wasserhell;… …   Herders Conversations-Lexikon

  • obsidian — (n.) dark, hard volcanic rock, 1650s, from L. obsidianus, misprint of Obsianus (lapis) (stone) of Obsius, name of a Roman alleged by Pliny to have found this rock in Ethiopia …   Etymology dictionary

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