igneous
Basalt with Limonite stains
Extrusive mafic igneous rock; Limonite (FeO(OH)·nH2O)
Hardness: 6 (Mohs scale), Color: Dark grey to charcoal with yellow-brown oxidation, Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained), Cleavage: None/Conchoidal fracture
Identified More igneous →
Explore Basalt with Limonite stains in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6 (Mohs scale), Color: Dark grey to charcoal with yellow-brown oxidation, Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained), Cleavage: None/Conchoidal fracture
Formation & geological history
Formed from the rapid cooling of magnesium and iron-rich lava at the Earth's surface. The orange-brown staining is caused by the chemical weathering and hydration of iron-rich silicate minerals (like olivine or pyroxene) into limonite.
Uses & applications
Primary use in construction as aggregate, road base, and concrete. In small specimens, it is used for geological teaching and children's starter collections.
Geological facts
Basalt is the most common rock type on the Earth's surface and actually makes up most of the ocean floor. It is also found in abundance on the Moon and Mars.
Field identification & locations
Identify by its dark, heavy, fine-grained mass and the presence of rusty oxidation. Common in volcanic regions worldwide (e.g., Pacific Northwest USA, Iceland, Hawaii). Collectors look for vesicles or 'holes' containing secondary crystals like zeolites.
