igneous
Diorite with Xenolith
Phaneritic Intermediate Plutonic Rock
Hardness: 6-7 Mohs; Color: Salt and pepper (black and white/gray); Luster: Sub-vitreous to dull; Structure: Phaneritic (coarse-grained crystals); Cleavage: Two directions at 60/120 degrees for amphiboles; SG: 2.8-3.0.
- Hardness
- 6-7 Mohs
- Color
- Salt and pepper (black and white/gray)
- Luster
- Sub-vitreous to dull
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Physical properties
Hardness: 6-7 Mohs; Color: Salt and pepper (black and white/gray); Luster: Sub-vitreous to dull; Structure: Phaneritic (coarse-grained crystals); Cleavage: Two directions at 60/120 degrees for amphiboles; SG: 2.8-3.0.
Formation & geological history
Formed by the slow cooling of intermediate magma deep within the Earth's crust (plutonic). The dark patch is likely a xenolith, a fragment of older rock that was incorporated into the magma without melting.
Uses & applications
Used primarily as crushed stone for road construction and drainage; in polished form, it is used for building facades, floor tiles, and countertops (often sold as 'black granite').
Geological facts
Diorite was used in ancient Egypt and Mesopotamia for sculptures and tablets because of its extreme hardness and durability; the Code of Hammurabi was inscribed on a diorite stele.
Field identification & locations
Identify by its 'salt and pepper' appearance with equal-ish parts light plagioclase and dark minerals like hornblende. Look for it in volcanic arcs and mountain roots. For collectors, well-defined xenolith inclusions add interest.
