igneous
Tumbled magnetite-bearing rock, likely basalt or gabbro
Magnetite (Fe₃O₄) in a mafic silicate matrix, probably basaltic or gabbroic
AI-generated identification · may be incorrectBlack, rounded and polished, with metallic to submetallic luster on magnetite-rich areas and pale gray crystalline patches; magnetite has Mohs hardness 5.5–6.5, cubic crystal structure, no cleavage, and strong magnetism. The light patches may be feldspar, quartz, or alteration minerals.
Identified More igneous →
Explore Tumbled magnetite-bearing rock, likely basalt or gabbro in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Black, rounded and polished, with metallic to submetallic luster on magnetite-rich areas and pale gray crystalline patches; magnetite has Mohs hardness 5.5–6.5, cubic crystal structure, no cleavage, and strong magnetism. The light patches may be feldspar, quartz, or alteration minerals.
Formation & geological history
Likely formed from cooling iron-rich mafic magma, with magnetite crystallizing during igneous solidification; basalt is volcanic and fine-grained, while gabbro is its coarse-grained intrusive equivalent. Exact geological age and locality cannot be determined from the image.
Uses & applications
Used as a small lapidary, teaching, or collector specimen; magnetite is an important iron ore, while basalt and gabbro are used as aggregate, dimension stone, and paving material.
Geological facts
A strong magnet test is the quickest confirmation of abundant magnetite; a gray streak and high density also support identification. The specimen appears tumbled or polished rather than naturally weathered.
Field identification & locations
Common in basaltic volcanic rocks, gabbro, metamorphic iron formations, and placer deposits worldwide, especially near volcanic or magnetite-rich regions. Inspect grain size and test magnetism to distinguish it from obsidian or slag.
