Chlorite schist from the Precambrian of Michigan, USA. (7.7 centimeters across at its widest)
<p>Chlorite is a common greenish to greenish-gray metamorphic mineral.  Actually, chlorite is a group of phyllosilicate minerals, a common example of which is chamosite chlorite: (Fe+2,Mg,Fe+3)5Al(Si3,Al)O10(OH,O)8 - iron magnesium hydroxy-oxy-aluminosilicate.  Chlorite is a common constituent of greenstone and various types of schist.  It is also a rock-forming mineral.  Seen here is a chlorite schist from the Michigamme Mine, an old iron mine in northern Michigan.  This material was a waste product.  When the mine was active, “black diamonds” in the chlorite schist unit were frustrating to miners - they were so abundant that they frequently damaged the rock-crushing equipment.  Michigamme Mine's black diamonds are actually chlorite pseudomorphs after garnet (see elsewhere in this photo album).
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Locality: Michigamme Mine, town of Michigamme, Upper Peninsula of Michigan, USA
James St. John
CC BY 2.0
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