igneous
Diorite (or salt-and-pepper granite pebble)
Phaneritic Igneous Rock (Intermediate Composition)
Hardness: 6-7 Mohs; Color: Mottled black and white (speckled); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarse-grained visible crystals); Clearing: Good in two directions (feldspars).
- Hardness
- 6-7 Mohs
- Color
- Mottled black and white (speckled)
- Luster
- Sub-vitreous to dull
Identified More igneous →
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Physical properties
Hardness: 6-7 Mohs; Color: Mottled black and white (speckled); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarse-grained visible crystals); Clearing: Good in two directions (feldspars).
Formation & geological history
Formed through the slow cooling of magma deep beneath the Earth's surface (intrusive). Commonly associated with volcanic arcs and subduction zones. This specimen appears water-worn, indicating it was transported by a river or glacier.
Uses & applications
Larger deposits are used for construction as crushed stone, floor tiles, and countertop material. Polished pebbles are used in decorative landscaping and aquarium gravel.
Geological facts
Diorite is often referred to as 'salt and pepper' rock due to its distinctive color mix. It was used by ancient civilizations, such as the Egyptians and Sumerians, for high-quality statues because of its extreme hardness.
Field identification & locations
Identify by looking for a 'salt and pepper' appearance with crystals of roughly equal size (no visible quartz usually separates it from granite). It is commonly found in mountain ranges and glacial deposits near ancient igneous activity.
