Basalt
Extrusive Igneous Rock / Basalt · Mineral Specimen / Rock
Crystal System
Microcrystalline to cryptocrystalline, typically aphanitic mass
Mineral Group
Silicates (primarily plagioclase feldspar and pyroxene)
Chemical Formula
Complex silicate mixture (primarily SiO2, Al2O3, FeO, MgO, CaO)
Formation Process
Igneous, formed from the rapid cooling of low-viscosity, mafic lava exposed at or very near the Earth's surface
About This Crystal
A dark grey, fine-grained rock specimen with a flat, tabular shape resembling a flake or small fragment, exhibiting an opaque appearance and a dull to sub-vitreous luster.
Physical Characteristics
Dark grey to black body color, white to grey streak, lacks distinct cleavage planes, exhibits uneven to conchoidal fracture, specific gravity around 2.8-3.0, brittle tenacity
Optical Properties
Opaque in hand specimen, anisotropic under petrographic microscope due to microscopic mineral grains
Hardness & Durability
Origin Region
Worldwide, commonly found in oceanic crust, volcanic islands, and continental flood basalt provinces
Hardness & Durability
Mohs hardness around 6, moderate toughness, chemically stable under normal conditions
Care & Maintenance
Clean with warm soapy water and a soft brush, store away from impacts to prevent chipping
Rarity & Value
Very common, low commercial value, primarily collected for educational or geological purposes
Special Characteristics
Often vesicular due to trapped gas bubbles during cooling, sometimes displays porphyritic texture with larger phenocrysts
Lore & History
Used historically by ancient civilizations for making tools, grinding stones, and construction materials due to its durability