Rock & Mineral Encyclopedia

Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.

Diorite

A coarse-grained intrusive rock with a distinctive salt-and-pepper look, the plutonic equivalent of andesite.

A coarse-grained, speckled intrusive rock built from quartz, feldspar, and mica, forming the bedrock of the continents.

A dense, coarse-grained ultramafic rock rich in olivine that makes up most of the Earth's upper mantle.

A coarse-grained intrusive igneous rock dominated by alkali feldspar with little or no quartz.

A common coarse-grained intrusive rock like granite but richer in plagioclase than potassium feldspar.

A coarse-grained mafic plutonic rock similar to gabbro but with orthopyroxene as the dominant pyroxene instead of clinopyroxene.

Coarse-grained gabbro that has been metamorphosed, partly recrystallizing into amphibole, plagioclase, and other metamorphic minerals.

A fine-grained clastic rock of silt-sized grains, intermediate between sandstone and mudstone, with a gritty feel.

A coarse-grained, feldspar-free plutonic rock composed mainly of nepheline and sodic pyroxene, the intrusive equivalent of nephelinite.

A coarse-grained alkali syenite of perthitic feldspar with sodic pyroxene or amphibole and minor nepheline, from Pulaski County, Arkansas.

A group of coarse, water-rich plutonic rocks dominated by large hornblende crystals set in feldspar, intermediate between lamprophyre and diorite.

A silver-white cobalt arsenic sulfide that is a leading ore of cobalt, forming bright metallic cubic and pyritohedral crystals.

A nodular rhyolite geode-like ball whose plain exterior hides a star-shaped agate or chalcedony core when cut.

A regional Russian name for a moonstone-like plagioclase from the White Sea coast, prized for its bluish, slightly iridescent schiller.