igneous
Diorite (River Pebble)
Phaneritic Intermediate Igneous Rock (Diorite)
Hardness: 6-7 Mohs; Color: Salt-and-pepper (mottled grey, black, and white); Luster: Dull (weathered); Crystal structure: Phaneritic (medium-grained); Cleavage: Two directions at nearly 90 degrees in feldspar components; Specific gravity: 2.8-3.0
- Hardness
- 6-7 Mohs
- Color
- Salt-and-pepper (mottled grey, black, and white)
- Luster
- Dull (weathered)
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Physical properties
Hardness: 6-7 Mohs; Color: Salt-and-pepper (mottled grey, black, and white); Luster: Dull (weathered); Crystal structure: Phaneritic (medium-grained); Cleavage: Two directions at nearly 90 degrees in feldspar components; Specific gravity: 2.8-3.0
Formation & geological history
Formed by the slow cooling of magma beneath the Earth's surface (intrusive plume); this specific specimen has been rounded and smoothed by water erosion in a high-energy environment like a river or beach.
Uses & applications
Used as a crushed stone for construction, architectural facings, and as decorative river stones in landscaping. Historically used for carving hard stone sculptures (e.g., the Code of Hammurabi).
Geological facts
Diorite is often called 'salt and pepper rock' due to its distinct mix of light plagioclase feldspar and dark minerals like hornblende or biotite. It is chemically intermediate between granite and gabbro.
Field identification & locations
Identify in the field by its speckled 'salt and pepper' appearance and lack of visible quartz compared to granite. It is commonly found in mountain roots (batholiths) and as smooth pebbles in riverbeds or coastal areas.
