noun[mass noun] Geology
Granite that is recognizable as crystalline only under a microscope.
- This is a coarsegrained biotite gneiss with an average granodioritic composition, that is generally fairly homogeneous but locally shows gneissic banding, and is intruded by veins of microgranite and pegmatite.
- The age of the Carrock microgranite provides further evidence that both calc-alkaline and tholeiitic magmas were available during Caradoc magmatism in the Lake District.
- The microgranite has a felsitic groundmass containing microphenocrysts of albite and orthoclase along with phenocrysts of corroded quartz and sporadic dihedral garnet; zircon and apatite are conspicuous accessory minerals.
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