igneous
Diorite (River Pebble)
Intermediate plutonic igneous rock
Hardness 6-7 on Mohs scale. Color is grayish with a characteristic 'salt and pepper' appearance caused by dark amphibole/biotite specs embedded in a lighter plagioclase feldspar matrix. Dull to earthy luster on weather-worn surface, non-foliated, fine-to-medium grained texture.
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Physical properties
Hardness 6-7 on Mohs scale. Color is grayish with a characteristic 'salt and pepper' appearance caused by dark amphibole/biotite specs embedded in a lighter plagioclase feldspar matrix. Dull to earthy luster on weather-worn surface, non-foliated, fine-to-medium grained texture.
Formation & geological history
Formed through the slow cooling and crystallization of intermediate magma beneath the Earth's surface (intrusive igneous). Subsequently eroded, rounded, and smoothed by stream or river transport.
Uses & applications
Commonly used in construction as crushed stone, road base, and ballast. Polished diorite is used for countertops, monuments, and decorative stone carvings.
Geological facts
Diorite is famous historically for being used to carve hard ancient sculptures and steles, including the famous Code of Hammurabi, due to its extreme durability and fine grain.
Field identification & locations
Look for a smooth, water-worn pebble featuring an even distribution of dark (mafic) and light (felsic) minerals without significant quartz content. Found abundantly in riverbeds, glacial deposits, and mountainous igneous zones.
