igneous
Diorite
Diorite
Hardness: 6-7 Mohs; Color: Salt and pepper (mottled black and white/gray); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.8-3.0.
- Hardness
- 6-7 Mohs
- Color
- Salt and pepper (mottled black and white/gray)
- Luster
- Sub-vitreous to dull
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Physical properties
Hardness: 6-7 Mohs; Color: Salt and pepper (mottled black and white/gray); 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 magma beneath the Earth's surface in volcanic arc and mountain-building regions. It often occurs as large intrusions like batholiths.
Uses & applications
Primarily used in construction as crushed stone or 'black granite ' for road base and buildings. High-quality specimens are polished for countertops, floor tiles, and ornamental stonework.
Geological facts
In ancient Egypt, diorite was so valued for its hardness that it was used to carve other stones and for creating statues of pharaohs, such as the famous statue of Khafre.
Field identification & locations
Identify by its coarse grain and nearly equal parts of light plagioclase feldspar and dark minerals (hornblende/biotite). Commonly found in subduction zones like the Andes or the Alps.
