metamorphic
Khondalite
Garnet-Sillimanite-Graphite Gneiss
Hardness: 6.5-7.5 (due to garnet/quartz); Color: Reddish brown to grey with visible pinkish-red garnets; Luster: Vitreous to dull; Structure: Foliated schistose or gneissose; Common minerals: Quartz, garnet, sillimanite, feldspar, and graphite.
- Hardness
- 6
- Color
- Reddish brown to grey with visible pinkish-red garnets
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6.5-7.5 (due to garnet/quartz); Color: Reddish brown to grey with visible pinkish-red garnets; Luster: Vitreous to dull; Structure: Foliated schistose or gneissose; Common minerals: Quartz, garnet, sillimanite, feldspar, and graphite.
Formation & geological history
Formed under high-grade regional metamorphism (granulite facies) of pelitic (clay-rich) sediments during the Proterozoic Era. This rock is a defining component of the Eastern Ghats Mobile Belt.
Uses & applications
Extensively used as building stone, for decorative facades in temples and monuments (historically used in the Sun Temple at Konark), and as an abrasive material.
Geological facts
Named after the 'Khond' tribe of Odisha and Andhra Pradesh, India, where these rocks were first described. It is the signature rock type of the Eastern Ghats.
Field identification & locations
Located at 17.7°N, 83.3°E (near Visakhapatnam, Andhra Pradesh), this specimen is in the heart of its type-locality. Identified by its 'pencil-like' sillimanite needles and reddish garnet porphyroblasts against a weathered brownish background.
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