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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 ]
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 with a conchoidal fracture, some weathering, and rust-red coloring. Obsidian is volcanic glass; often black and opaque. Caldera is the type locality for a resurgent dome caldera, the formation of which was first developed by C.S. Ross, R.L. Smith, and R.A. Bailey during field work at Valles in the 1960s. [19]
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]
The volcano was in continuous eruption from October 2004, but this eruption consisted in large part of a gradual extrusion of lava forming a dome in the crater. On January 16, 2008, steam began seeping from a fracture on top of the lava dome. Associated seismic activity was the most noteworthy since 2004.
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.
Lacking a central volcanic cone, the Svartsengi volcanic system consists of a set of fissures, cones and volcanic craters aligned over 30 km (19 mi) in length and 7 km (4.3 mi) in width, oriented north-east to south-west and surrounded by fields of lava: [3] Þorbjörn (243 m (797 ft)), Hagafell (158 m (518 ft)), Sundhnúkur 134 m (440 ft) (Sundhnúksgígar means the associated crater row ...
The glass shards (mostly brown) sometimes become welded together when the deposit is still hot, and can be deformed by flow and compaction about crystal fragments (clear). Ignimbrite is primarily composed of a matrix of volcanic ash ( tephra ) which is composed of shards and fragments of volcanic glass, pumice fragments, and crystals.