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(adj. drusy)

A cavity (vugh) in an igneous rock or a mineral vein into which euhedral (well-formed) crystals of the rock or mineral vein project, or the crystals themselves. The cavity represents a volume of late-stage, vapour-rich magma trapped by the rock crystallizing around it. Crystals can grow freely into this medium and hence crystallize in perfect forms (e.g. smokey quartz in granite) to give well-shaped crystal faces. The word is German, Druse meaning decayed or weathered ore.

Subjects: Earth Sciences and Geography.

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