igneous
Orbicular gabbro (likely oceanic orbicular rock)
Orbicular gabbro, composed chiefly of plagioclase feldspar and pyroxene, with concentric orbicules
AI-generated identification · may be incorrectDark gray, coarse-grained, with pale rounded orbicules and blocky white feldspar crystals; vitreous to dull luster, no consistent cleavage as a rock, hardness about 6–7, and specific gravity roughly 2.8–3.1.
Identified More igneous →
Explore Orbicular gabbro (likely oceanic orbicular rock) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray, coarse-grained, with pale rounded orbicules and blocky white feldspar crystals; vitreous to dull luster, no consistent cleavage as a rock, hardness about 6–7, and specific gravity roughly 2.8–3.1.
Formation & geological history
A rare intrusive igneous rock formed when mafic magma crystallized slowly, with repeated mineral growth around nuclei producing orbicules; specimens are generally Precambrian to Phanerozoic, depending on locality.
Uses & applications
Primarily a collector’s specimen and decorative stone; attractive cut surfaces may be used for lapidary objects, bookends, or ornamental slabs, but it has little bulk industrial use.
Geological facts
The circular structures are orbicules—concentric growth zones formed by rhythmic crystallization and magma movement, not fossils. Similar material is marketed under locality names such as orbicular gabbro or orbicular diorite.
Field identification & locations
Identify it by its dark mafic matrix, pale feldspar-rich rounded patterns, and coarse interlocking texture; confirm with a hand lens and feldspar hardness test. Notable occurrences include Finland, Madagascar, Corsica, and parts of Scandinavia.
