igneous
Diorite (Salt and Pepper Rock)
Diorite
Hardness: 6-7 (Mohs scale), Color: Mottled black and white (salt and pepper appearance), Luster: Dull to sub-vitreous, Structure: Phaneritic (coarse-grained), Specific Gravity: 2.8-3.0
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Mottled black and white (salt and pepper appearance), Luster: Dull to sub-vitreous, Structure: Phaneritic (coarse-grained), Specific Gravity: 2.8-3.0
Formation & geological history
Formed by the slow cooling of intermediate magma underground, typically occurring in volcanic arcs and mountain building zones above subduction zones.
Uses & applications
Used primarily as crushed stone for road construction and as a dimension stone for architectural facings, floor tiles, and grave markers (often sold as 'black granite').
Geological facts
Diorite is extremely hard and was frequently used by ancient civilizations, such as the Egyptians and Sumerians, to create sculptures and durable vessels because of its resistance to weathering.
Field identification & locations
Identified by its medium to coarse-grained texture and approximately equal mix of light plagioclase feldspar and dark minerals like hornblende or biotite. It lacks the visible quartz typical of granite.
