Rock & Mineral Encyclopedia

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

Granodiorite

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

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

A quartz-rich plutonic rock dominated by plagioclase feldspar with little alkali feldspar, closely related to granodiorite and quartz diorite.

A dense, black, mid-rank coal with high energy content, widely used for power generation and to make coke for steelmaking.

A combustible black sedimentary rock formed from ancient plant matter and burned for centuries as a primary fossil fuel.

A rare zirconium-bearing garnet that crystallizes in carbonatites and alkaline rocks, first described from Magnet Cove, Arkansas.

An opaque, snow-white variety of quartz whose milky color comes from countless tiny gas and fluid inclusions.

Iron-stained sandstone whose red color comes from hematite coatings, formed in oxidizing desert, river, and coastal environments.

An extremely common calcium carbonate mineral that comes in nearly every color and shows strong double refraction in clear crystals.

An orange-to-rust colored variety of natural volcanic glass whose warm tone comes from iron oxide staining within the obsidian.

A translucent, soft blue variety of microcrystalline quartz whose color comes from light scattering through its fine structure.

A chromium-rich pyrope garnet whose intense blood-red color comes from chromium, often mined from ant hills and kimberlite weathering.

A deep blue beryl whose intense color comes from radiation-induced color centers and tends to fade in light, named after the Maxixe mine in Brazil.