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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 ]
Volcanic glass is the amorphous (uncrystallized) ... Most commonly, volcanic glass refers to obsidian, a rhyolitic glass with high silica (SiO 2) content. [7]
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.
Helenite, also known as Mount St. Helens obsidian, emerald obsidianite, and ruby obsidianite, is a glass made from the fused volcanic rock dust from Mount St. Helens and marketed as a gemstone. [ 1 ] [ 2 ] Helenite was first created accidentally after the eruption of Mount St. Helens in 1980 .
Obsidian – Naturally occurring volcanic glass; Pegmatite – Igneous rock with very large interlocked crystals; Peridotite – Coarse-grained ultramafic igneous rock type; Phonolite – Uncommon extrusive rock – A silica-undersaturated volcanic rock; essentially similar to nepheline syenite
The Glass Mountain Ridge forms the northeast boundary of Long Valley Caldera. It consists of a sequence of lava domes, flows, and welded pyroclastic flows of rhyolite composition that were erupted between 2.1 and 0.8 million years ago. [6] Obsidian, a naturally occurring volcanic glass, can be found on the mountain. [7]
Ancient Greek glass amphora from the Hellenistic period.. Naturally occurring glass, especially the volcanic glass obsidian, has been used by many Stone Age societies across the globe for the production of sharp cutting tools and, due to its limited source areas, was extensively traded.
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 ...