igneous
Diorite
Diorite (Phaneritic intermediate plutonic rock)
Hardness: 6-7 (Mohs scale); Color: Black and white (salt and pepper appearance); Luster: Submetallic to dull; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.8-3.0
- Hardness
- 6-7 (Mohs scale)
- Color
- Black and white (salt and pepper appearance)
- Luster
- Submetallic to dull
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Black and white (salt and pepper appearance); Luster: Submetallic to dull; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.8-3.0
Formation & geological history
Formed by the slow cooling of magma deep beneath the Earth's surface (intrusive plutonic). Usually occurs in volcanic arcs and above subduction zones during mountain-building events.
Uses & applications
Used in construction as crushed stone or 'drain rock', building facades, floor tiles, and historically for sculpture (e.g., Code of Hammurabi). Too coarse for high-end jewelry but sometimes used in lapidary work.
Geological facts
Diorite is often called 'Black Granite' in the stone trade, though geologically distinct. The ancient Egyptians used it extensively for hard-stone carvings and statues due to its extreme durability.
Field identification & locations
Identify by its 'salt and pepper' look where dark minerals (hornblende/biotite) and light minerals (plagioclase feldspar) are roughly equal in size. Commonly found in large batholiths such as the Andes Mountains.
