ES2 Metamorphic Rocks - Metamorphic Microstructures #13
Commonly a porphyroblast will grow by addition of material to its outer surface more rapidly than unwanted material (such as matrix quartz grains) can be removed from the interface. The porphyroblast traps the material as inclusions, forming a poikiloblast. In the example, the left-hand side shows a poikiloblast of colourless, moderate-relief andalusite, with inclusions mainly of quartz and biotite, while on the right a high relief staurolite poikiloblast is packed with tiny quartz inclusions.
Field of view is 3 mm across.
Andalusite-staurolite schist, Banff coast, NE Scotland. Sample BB1.
Left arrow Previous page Up arrow Back to Index Right arrow Next page
DJW - August 1997