igneous
Diorite
Diorite (Intermediate intrusive igneous rock)
Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper appearance consisting of black and white minerals. Luster: Vitreous to dull. Crystal structure: Phaneritic (coarse-grained). Cleavage: Two directions (mostly from feldspar and amphibole). Specific gravity: 2.8 - 3.0.
- Hardness
- 6-7 on Mohs scale
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper appearance consisting of black and white minerals. Luster: Vitreous to dull. Crystal structure: Phaneritic (coarse-grained). Cleavage: Two directions (mostly from feldspar and amphibole). Specific gravity: 2.8 - 3.0.
Formation & geological history
Formed through the slow cooling of magma beneath the Earth's surface in volcanic arches and mountain-building zones. Chemically, it is intermediate between granite and gabbro, often associated with subduction zones.
Uses & applications
Used in construction as crushed stone for roads and drainage, as dimension stone for architectural facades, and as base material for monuments. Historically used by ancient civilizations for sculpture (e.g., the Code of Hammurabi).
Geological facts
Diorite is often mistakenly called 'black granite' in the commercial stone trade. One of the most famous diorite sculptures is the 'Code of Hammurabi' stele, chosen for its extreme durability which preserved the laws for millennia.
Field identification & locations
Identify in the field by its phaneritic texture and roughly equal mix of light (Plagioclase feldspar) and dark (Hornblende/Biotite) minerals. Found in large batholiths in the Andes, the Alps, and coastal ranges of North America. It is harder than marble but easier to carve than granite.
