Igneous
Diorite (Polished Cobble)
Diorite (Intermediate intrusive igneous rock)
Hardness: 6-7 on Mohs scale; Color: Mottled 'salt and pepper' appearance (black, dark green, and white/grey); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.8 - 3.0.
- Hardness
- 6-7 on Mohs scale
- Luster
- Sub-vitreous to dull
Identified More igneous →
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Mottled 'salt and pepper' appearance (black, dark green, and white/grey); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.8 - 3.0.
Formation & geological history
Formed by the slow cooling of silicate magma below the Earth's surface, typically in volcanic arcs or above subduction zones. This specimen appears water-worn or mechanically polished from an ancient riverbed or glacial deposit.
Uses & applications
Used primarily as crushed stone for road construction, as architectural 'black granite' for countertops and floor tiles, and occasionally for carving or lapidary work.
Geological facts
Diorite was extremely popular in Ancient Egypt and Mesopotamia for sculptures because of its extreme hardness; the famous Code of Hammurabi was inscribed on a diorite stele.
Field identification & locations
Identify by its 'salt and pepper' mixture of light plagioclase feldspar and dark amphibole or pyroxene minerals. Found in large mountain ranges such as the Andes, or as glacial erratics in the Northern US and Europe.
