igneous
Diorite
Diorite (intermediate intrusive igneous rock)
Hardness: 6-7 (Mohs scale), Color: salt-and-pepper appearance (mixture of black/dark green and white), Luster: dull to sub-vitreous, Crystal structure: phaneritic (coarse-grained visible crystals), Specific Gravity: 2.8-3.0
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Physical properties
Hardness: 6-7 (Mohs scale), Color: salt-and-pepper appearance (mixture of black/dark green and white), Luster: dull to sub-vitreous, Crystal structure: phaneritic (coarse-grained visible crystals), Specific Gravity: 2.8-3.0
Formation & geological history
Formed by the slow cooling of magma beneath the Earth's surface (intrusive). It is an intermediate rock between granite and gabbro, often found in volcanic arcs and mountain-building zones (orogenic belts).
Uses & applications
Used primarily as crushed stone for road construction and aggregate. High-quality specimens are polished for use as dimension stone (granite-like countertops), monuments, and decorative facing on buildings.
Geological facts
Diorite is often called 'Black Granite' in the commercial stone trade. The famous Code of Hammurabi, a Babylonian law code, was inscribed on a 7-foot tall pillar of polished diorite.
Field identification & locations
Identify in the field by its characteristic 'salt and pepper' grainy texture with roughly equal amounts of dark minerals (hornblende/biotite) and light minerals (plagioclase feldspar). It lacks the visible quartz typical of granite. Commonly found in massive plutons.
