igneous
Diorite
Diorite (intermediate plutonic rock)
Hardness: 6-7 (Mohs scale), Color: salt-and-pepper (white plagioclase with dark hornblende/biotite), Luster: dull to vitreous, Texture: phaneritic (coarse-grained).
- Luster
- dull to vitreous, Texture: phaneritic (coarse-grained)
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Physical properties
Hardness: 6-7 (Mohs scale), Color: salt-and-pepper (white plagioclase with dark hornblende/biotite), Luster: dull to vitreous, Texture: phaneritic (coarse-grained).
Formation & geological history
Formed from the slow cooling of magma beneath the Earth's surface in volcanic arcs and subduction zones. It has an intermediate composition between granite and gabbro.
Uses & applications
Historically used for sculpture and inscriptions (like the Code of Hammurabi); currently used as crushed stone for roads or as polished 'black granite' in construction.
Geological facts
Diorite is extremely tough and was used by ancient civilizations for intricate carvings because of its durability. It is often confused with granite but lacks significant quartz.
Field identification & locations
Identify by its characteristic speckled appearance and lack of visible quartz crystals. Frequently found in well-worn river pebbles or coastal cobbles like the one pictured.
