Pitchstone

Pitchstone is a dull black glassy volcanic rock formed when viscous lava or magma cools quickly. It is similar to but coarser than obsidian. It is a volcanic glass with a conchoidal fracture (like glass), a resinous lustre, or silky in some cases, and a variable composition. Its colour may be mottled, streaked, or uniform brown, red, green, gray, ...
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Pitchstone

• (n.) An igneous rock of semiglassy nature, having a luster like pitch.
Found on http://thinkexist.com/dictionary/meaning/pitchstone/

pitchstone

noun dark acid granitic glass
Found on https://www.encyclo.co.uk/local/20974

Pitchstone

Pitch'stone` noun (Geol.) An igneous rock of semiglassy nature, having a luster like pitch.
Found on http://www.encyclo.co.uk/webster/P/96

pitchstone

a volcanic glass with a conchoidal fracture (like glass), a resinous lustre, and a variable composition. Its colour may be mottled, streaked, or ...
Found on http://www.britannica.com/eb/a-z/p/73

Pitchstone

Pitchstone is a dark, glassy igneous rock produced by the rapid cooling of lava. It is composed essentially of feldspar and quartz and is a natural glass, the glass forming because the rock cools too quickly for the minerals to form into crystals. Pitchstone is closely related to obsidian, but where pitchstone has cooled more slowly than obsidian, ...
Found on http://www.probertencyclopaedia.com/browse/HP.HTM

pitchstone

[n] - dark acid granitic glass
Found on http://www.webdictionary.co.uk/definition.php?query=pitchstone
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