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Obsidian was valued in Stone Age cultures because, like flint, it could be fractured to produce sharp blades or arrowheads in a process called knapping. Like all glass and some other naturally occurring rocks, obsidian breaks with a characteristic conchoidal fracture. It was also polished to create early mirrors.
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 ...
Phaneritic (phaner = visible) textures are typical of intrusive igneous rocks, these rocks crystallized slowly below Earth's surface. As magma cools slowly the minerals have time to grow and form large crystals. The minerals in a phaneritic igneous rock are sufficiently large to see each individual crystal with the naked eye.
Trace Element Analysis (Obsidian) - This method of analysis involves measurements of the elemental composition of obsidian blades using the most common method of X-ray fluorescence (XRF). This allows researchers to select chemical compounds and compare them to known geological sources and identify patterns of procurement, trade, and distribution.
Chert, obsidian, quartzite, quartz, and many other rocks and minerals were commonly used to make points in North America. The oldest projectile points found in North America were long thought to date from about 13,000 years ago, during the Paleo-Indian period , however recent evidence suggests that North American projectile points may date to ...
The following is a list of rock types recognized by geologists.There is no agreed number of specific types of rock. Any unique combination of chemical composition, mineralogy, grain size, texture, or other distinguishing characteristics can describe a rock type.
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It often occurs in amorphous or fine-grained mineraloids such as flint, opal or obsidian, but may also occur in crystalline minerals such as quartz. Subconchoidal fracture is similar to conchoidal fracture, but with less significant curvature. Note that obsidian is an igneous rock, not a mineral, but it does illustrate conchoidal fracture well.