igneous
Diorite
Diorite (Intermediate intrusive igneous rock)
Hardness: 6-7 (Mohs scale); Color: 'Salt and pepper' (mottled black and white); Luster: Sub-vitreous to dull; Structure: Phaneritic (coarse-grained); Cleavage: Two directions (amphibole and feldspar); Specific Gravity: 2.8-3.0.
- Hardness
- 6-7 (Mohs scale)
- Color
- 'Salt and pepper' (mottled black and white)
- Luster
- Sub-vitreous to dull
Identified More igneous →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6-7 (Mohs scale); Color: 'Salt and pepper' (mottled black and white); Luster: Sub-vitreous to dull; Structure: Phaneritic (coarse-grained); Cleavage: Two directions (amphibole and feldspar); 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 found in batholiths and dikes.
Uses & applications
Used primarily as a crushed stone for construction, road base, and drainage. High-quality specimens are polished for use as building facades, countertops, and floor tiles. Historically used for carving, most notably the Code of Hammurabi.
Geological facts
Diorite is often called 'salt and pepper rock' because of its distinct mix of light plagioclase feldspar and dark minerals like hornblende. It is the plutonic equivalent of the volcanic rock andesite.
Field identification & locations
Identify in the field by its coarse grain and roughly equal mix of light and dark minerals. Unlike granite, it lacks significant quartz (less than 5%). Commonly found in volcanic arc settings like the Andes or the Cascades.
