igneous
Diorite
Diorite (intermediate intrusive igneous rock)
Hardness: 6-7 Mohs. Color: Salt-and-pepper (speckled black and white). Luster: Dull to sub-vitreous. Structure: Phaneritic (coarse-grained). Composition: Primarily plagioclase feldspar, hornblende, and biotite. Specific Gravity: 2.8-3.0.
- Hardness
- 6-7 Mohs
- Color
- Salt-and-pepper (speckled black and white)
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 Mohs. Color: Salt-and-pepper (speckled black and white). Luster: Dull to sub-vitreous. Structure: Phaneritic (coarse-grained). Composition: Primarily plagioclase feldspar, hornblende, and biotite. Specific Gravity: 2.8-3.0.
Formation & geological history
Formed by the slow cooling of magma beneath the Earth's surface in volcanic arcs and mountain-building zones (subduction zones). It is typically intrusive and often occurs as large plutons or batholiths.
Uses & applications
Used primarily as crushed stone for road construction and drainage. It can be polished as 'black granite' for countertops, flooring, and decorative building stone. Historically used by ancient civilizations for sculpture due to its durability.
Geological facts
The famous Code of Hammurabi was inscribed on a large diorite stele over 7 feet tall. It is often confused with gabbro or granite, but contains more feldspar than gabbro and less quartz than granite.
Field identification & locations
Identify in the field by its distinctive 'salt-and-pepper' speckled appearance with visible interlocking crystals. Common in the Andes Mountains of South America and various mountain ranges in North America. Collectors look for large, well-defined hornblende crystals.
