AskDefine | Define pitchstone

Dictionary Definition

pitchstone n : dark acid granitic glass

User Contributed Dictionary

English

Noun

pitchstone
  1. a natural glass, that is rich in microscopic crystalites, formed by the rapid cooling of lava or magma

Extensive Definition

Pitchstone is a dull black glassy volcanic rock formed when lava cools swiftly. It is similar to but coarser than obsidian.
The ridge of An Sgurr on the Isle of Eigg was originally formed as a lava flow in a valley. Pitchstone is very resistant to erosion.
pitchstone in German: Pechstein
pitchstone in Spanish: Vidrio volcánico
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