Tachylyte
Also spelled �tachylite� glassy igneous rocks low in silica, such as basalt or diabase. Tachylytes are black with a pitchlike or resinous lustre; in thin sections they are characteristically brown and translucent, and the glass is crowded with granules of magnetite. Tachylytes are found only under conditions that imply rapid cooling, and they are much less common than are the corresponding
posted by AutomaticBranch @ 3:41 AM
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