metamorphic
Garnet-bearing metamorphic rock
Garnet amphibolite or garnet–mica schist; chiefly almandine garnet (Fe₃Al₂Si₃O₁₂) with amphibole, mica, quartz, and feldspar
AI-generated identification · may be incorrectDark gray-green, coarse and strongly foliated, with wine-red to brown garnet crystals and a dull to vitreous luster. Garnet hardness is about 6.5–7.5 Mohs; matrix minerals range roughly 2–7, and garnet commonly shows no cleavage with granular crystal structure.
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Physical properties
Dark gray-green, coarse and strongly foliated, with wine-red to brown garnet crystals and a dull to vitreous luster. Garnet hardness is about 6.5–7.5 Mohs; matrix minerals range roughly 2–7, and garnet commonly shows no cleavage with granular crystal structure.
Formation & geological history
Formed when basaltic or clay-rich protoliths underwent medium- to high-grade regional metamorphism during mountain building. The specimen’s exact geological age cannot be determined visually; such rocks occur from Precambrian to younger orogenic terrains.
Uses & applications
Primarily a collector specimen; garnet may be used as an abrasive, while similar massive rocks can serve as decorative stone or aggregate, though this piece is not suitable for construction grading.
Geological facts
Red garnet porphyroblasts are useful indicators of metamorphic pressure and temperature. Dark amphibole-rich varieties may preserve evidence of former volcanic crust.
Field identification & locations
Look for embedded, rounded to angular red garnets within a foliated dark matrix; a streak, hardness, and density test can distinguish garnet from glass or red feldspar. Common sources include metamorphic belts in India, Madagascar, Norway, the Adirondacks, and western North America.
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