igneous
Diorite (Salt and Pepper Rock)
Diorite
Hardness: 6-7 (Mohs); Color: Black and white (mottled); Luster: Subvitreous to dull; Crystal structure: Phaneritic (coarsegrained) equigranular; Specific gravity: 2.8-3.0.
- Hardness
- 6-7 (Mohs)
- Color
- Black and white (mottled)
- Luster
- Subvitreous to dull
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Physical properties
Hardness: 6-7 (Mohs); Color: Black and white (mottled); Luster: Subvitreous to dull; Crystal structure: Phaneritic (coarsegrained) equigranular; Specific gravity: 2.8-3.0.
Formation & geological history
Formed from the slow cooling of magma beneath the Earth's surface in volcanic arcs and mountain-building zones (subduction zones). Often Mesozoic to Cenozoic in age.
Uses & applications
Used as a base material in construction of roads, buildings, and parking areas; as a decorative stone (countertops, tiles, paving) and for sculpture due to its durability.
Geological facts
Famous ancient Egyptian sculptures, including the Code of Hammurabi, were carved into diorite because of its extreme hardness and durability. It is chemically intermediate between granite and gabbro.
Field identification & locations
Identify in the field by its distinctive 'salt and pepper' appearance with roughly equal parts dark mafic minerals (hornblende/biotite) and light plagioclase feldspar. Common in batholiths like the Sierra Nevada.
