Orbicular granites are characterized by having large, concentrically layered, spheroidal to subspheroidal masses with radiating crystals.  The rounded masses are called orbs, or orbicles.  Shown below are samples of a Precambrian orbicular granodiorite from Western Australia.


The matrix is granodiorite (K-feldspar, plagioclase feldspar, quartz, mafic mineral(s)), and the orbicles are composed of plagioclase feldspars, hornblende amphibole, and biotite mica.


This material is mid-Neoarchean in age (2.687 billion years old) and comes from a quarry in the vicinity of Warroan Hill, a little west of Boogardie, west of Mt. Magnet & east-northeast of Geraldton, in the western part of Western Australia.






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