igneous
Black Granite (Basalt or Gabbro)
Mafic Igneous Rock (primarily Plagioclase and Pyroxene)
Hardness: 6-7 Mohs; Color: Dark grey to black with light speckling; Luster: Vitreous when polished; Crystal Structure: Phaneritic (medium-grained) to Aphanitic; Specific Gravity: 2.7-3.3
- Hardness
- 6-7 Mohs
- Color
- Dark grey to black with light speckling
- Luster
- Vitreous when polished
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to black with light speckling; Luster: Vitreous when polished; Crystal Structure: Phaneritic (medium-grained) to Aphanitic; Specific Gravity: 2.7-3.3
Formation & geological history
Formed from the slow or rapid cooling of magnesium and iron-rich (mafic) magma. Depending on grain size, it is either an intrusive Gabbro or an extrusive Basalt. Found in oceanic crust and continental volcanic provinces.
Uses & applications
Extensively used in construction for countertops, flooring, monuments, and as crushed stone for road base and railway ballast.
Geological facts
In the commercial stone industry, almost any dark, hard igneous rock is sold as 'Black Granite,' although scientifically, true granite must contain at least 20% quartz and be felsic.
Field identification & locations
Identify by its dark color (mafic composition), density, and lack of visible quartz. Common in volcanic regions and often used as a durable building material in urban environments.
