igneous
Orbicular granite (likely orbicular diorite)
Orbicular granitoid; chiefly quartz, feldspar, biotite/hornblende, with orbicules of concentric feldspathic minerals
AI-generated identification · may be incorrectTypically Mohs 6–7, coarse-grained, dark green-black and cream with rounded concentric orbicules; vitreous to dull luster and no strong cleavage as a whole. The rounded, spotted texture is its defining feature.
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Physical properties
Typically Mohs 6–7, coarse-grained, dark green-black and cream with rounded concentric orbicules; vitreous to dull luster and no strong cleavage as a whole. The rounded, spotted texture is its defining feature.
Formation & geological history
A rare plutonic rock formed when magma crystallized slowly underground, with chemical layering around nuclei producing orbicules; examples are generally Precambrian to Paleozoic, depending on locality.
Uses & applications
Used mainly as polished cabochons, spheres, decorative stone, and collector specimens; too rare and variable for ordinary construction use.
Geological facts
Orbicular rocks are among the most distinctive granitic textures and are sometimes marketed as “orbicular granite,” “orbicular diorite,” or “orbicular jasper,” though the latter name can be misleading.
Field identification & locations
Identify by its interlocking crystalline matrix and rounded, often concentric light-dark patches rather than glassy or cryptocrystalline texture. Famous occurrences include Finland, Madagascar, Corsica, and California; exact mineral identification requires thin-section or laboratory testing.
