igneous
Diorite (or Gabbro/Gneiss stream pebble)
Diorite
Hardness 6-7 on Mohs scale; speckled black/dark green and white/cream color pattern ('salt and pepper' appearance); phaneritic (medium- to coarse-grained) texture; dull to vitreous luster; composition mainly of plagioclase feldspar and dark minerals like hornblende, augite, or biotite.
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Physical properties
Hardness 6-7 on Mohs scale; speckled black/dark green and white/cream color pattern ('salt and pepper' appearance); phaneritic (medium- to coarse-grained) texture; dull to vitreous luster; composition mainly of plagioclase feldspar and dark minerals like hornblende, augite, or biotite.
Formation & geological history
Formed through the slow cooling and crystallization of intrusive silicate magma deep beneath the Earth's surface, typically in volcanic arcs or subduction zones.
Uses & applications
Used as crushed stone for construction, road base, dimension stone for buildings, countertops, and decorative landscaping rock.
Geological facts
Diorite was used in ancient times for carving durable monuments and inscriptions due to its hardness; the famous Code of Hammurabi stela is carved on black diorite.
Field identification & locations
Identified in the field by its interlocking coarse grains and characteristic 'salt and pepper' mottled pattern without quartz dominance. Commonly found in stream beds, beach gravels, and mountain ranges around tectonic plate margins.
