igneous
Diorite (Salt and Pepper Rock)
Diorite
Hardness: 6-7 (Mohs scale), Color: Mottled black and white/gray, Luster: Vitreous to dull, Structure: Coarse-grained phaneritic texture, Cleavage: Good in two directions (feldspar) and two at 120/60 degrees (hornblende).
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Mottled black and white/gray, Luster: Vitreous to dull, Structure: Coarse-grained phaneritic texture, Cleavage: Good in two directions (feldspar) and two at 120/60 degrees (hornblende).
Formation & geological history
Formed by the slow cooling of silicate magma below the Earth's surface (intrusive). They are often found in volcanic arcs and mountain building zones (orogenic belts).
Uses & applications
Used in construction as crushed stone for roads and drainage, as dimension stone for building facades and countertops, and occasionally for carved statues and monuments.
Geological facts
Diorite was used in ancient Egypt for statues and sarcophagi because of its extreme toughness. The Code of Hammurabi was famously inscribed upon a diorite stele.
Field identification & locations
Identified by its 'salt and pepper' appearance caused by the mix of white plagioclase feldspar and dark minerals like hornblende or biotite. Commonly found in riverbeds as rounded pebbles.
