igneous
Basalt with Olivine Phenocrysts
Porphyritic Basalt (with (Mg, Fe)2SiO4)
Hardness: 6-7 (Mohs scale), Color: Dark grey to black matrix with olive-green or brownish inclusions, Luster: Vitreous to dull, Crystal structure: Orthorhombic (olivine), Cleavage: Indistinct, Specific Gravity: 2.8-3.4
Identified More igneous →
Explore Basalt with Olivine Phenocrysts in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6-7 (Mohs scale), Color: Dark grey to black matrix with olive-green or brownish inclusions, Luster: Vitreous to dull, Crystal structure: Orthorhombic (olivine), Cleavage: Indistinct, Specific Gravity: 2.8-3.4
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava (basaltic) either at or very near the Earth's surface during volcanic eruptions. Common in oceanic crust and volcanic islands.
Uses & applications
Used primarily as crushed stone for road base, concrete aggregate, and railroad ballast. Gem-quality olivine (peridot) is used in jewelry.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. When olivine crystals are large and clear enough, they are the source of the August birthstone, Peridot.
Field identification & locations
Identify in the field by its dark, dense sugary-textured matrix and the presence of small, glassy green 'sand-like' grains. It is commonly found in volcanic regions such as Hawaii, Iceland, or the Columbia River Plateau.
