igneous
Diorite (Salt and Pepper Rock)
Diorite (comprising Plagioclase Feldspar, Hornblende, and Biotite)
Hardness: 6–7 Mohs. Color: Speckled black and white (salt and pepper). Luster: Dull to sub-vitreous. Texture: Phaneritic (coarse-grained). Cleavage: Two directions at nearly 90 degrees (in feldspar grains). Specific Gravity: 2.8–3.0.
- Hardness
- 6–7 Mohs
- Color
- Speckled black and white (salt and pepper)
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6–7 Mohs. Color: Speckled black and white (salt and pepper). Luster: Dull to sub-vitreous. Texture: Phaneritic (coarse-grained). Cleavage: Two directions at nearly 90 degrees (in feldspar grains). Specific Gravity: 2.8–3.0.
Formation & geological history
Formed by the slow cooling of magma deep beneath the Earth's surface (intrusive/plutonic). Typically associated with volcanic arcs and subduction zones. This specific specimen has been further shaped by water erosion (river or beach pebble).
Uses & applications
Construction (crushed stone, base material), architectural stone (countertops, pavers), and historically used for carvings and sculptures due to its durability.
Geological facts
Diorite was used in ancient Egypt and Mesopotamia for sculptures; the famous Code of Hammurabi was inscribed on a massive basalt/diorite stele. It is often confused with Granite but contains little to no visible quartz.
Field identification & locations
Identify by its 'salt and pepper' appearance with crystals of roughly equal size. Unlike granite (which has pink/white/clear grains), diorite is strictly medium-to-dark grey and white. Commonly found in mountain ranges like the Andes or Cascade mountains.
