ES2 Metamorphic Rocks - Metamorphic Microstructures #16
Idioblastic (euhedral).
Showing good crystal shape. In rocks which approach textural equilibrium we do not usually expect minerals to develop good crystal faces. However, idioblastic texture is fairly common in porphyroblasts. This example is of staurolite in a metapelite. Despite being packed with inclusions, the crystal has a very regular outline. The other porphyroblasts (biotite with dark radiation haloes) show much poorer crystal outline (subhedral to anhedral).
Field of view is 2.5 mm across.
Andalusite-staurolite schist, Banff coast, NE Scotland. Sample BB1.
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DJW - August 1997