igneous
Diorite (or Gabbro / Pegmatitic Intrusive Rock)
Plagioclase-Amphibole Igneous Rock
Phaneritic (coarse-grained) texture displaying a 'salt and pepper' appearance. Contains white to grey plagioclase feldspar and dark green-black amphibole (hornblende) or pyroxene minerals. Hardness around 6-7 on Mohs scale, vitreous to dull luster, specific gravity 2.8-3.0.
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Physical properties
Phaneritic (coarse-grained) texture displaying a 'salt and pepper' appearance. Contains white to grey plagioclase feldspar and dark green-black amphibole (hornblende) or pyroxene minerals. Hardness around 6-7 on Mohs scale, vitreous to dull luster, specific gravity 2.8-3.0.
Formation & geological history
Formed through the slow cooling and crystallization of intermediate to mafic magma deep within the Earth's crust, typically in continental arcs and subduction zone environments.
Uses & applications
Used primarily as crushed stone for road construction, ballast, and aggregate, as well as dimension stone for counter tops, monuments, and decorative building facades (often sold commercially as 'black granite').
Geological facts
Ancient Egyptian sculptors preferred diorite for carving statues because of its extreme hardness and durability. Code of Hammurabi, one of the oldest deciphered writings of significant length in the world, was inscribed on a 7-foot tall diorite stele.
Field identification & locations
Identify in the field by its distinct speckling of interlocking white (feldspar) and dark green/black (hornblende/pyroxene) crystals without significant quartz content. Commonly found in mountain belts, batholiths, and volcanic arcs globally.
