Rock & Mineral Encyclopedia

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

Eltyubyuite

A rare chlorine-bearing iron garnet-supergroup mineral, the ferric analogue of wadalite, formed in high-temperature combustion-metamorphic rocks.

A chromium-dominant tourmaline related to dravite, producing intensely deep green to blackish-green crystals from chromium-rich metamorphic rocks.

A hard zinc-rich member of the spinel group, usually dark blue-green to black, forming octahedral crystals in metamorphic and pegmatitic rocks.

An extremely hard metamorphic rock formed from sandstone, made of fused quartz grains that break across rather than between the grains.

A dense, high-pressure metamorphic rock famous for its red garnets set in bright green pyroxene, formed deep within subduction zones.

A contact-metasomatic calc-silicate rock, essentially a skarn, formed where intrusions react with carbonate rocks and often host ore.

A calc-silicate rock formed by chemical exchange between magma and carbonate rock, often rich in garnet and economically important ore minerals.

A fine-grained, sodium-rich contact-metasomatic rock formed where shale is albitized next to intruding diabase or spilite.

A dull, resinous volcanic glass similar to obsidian but with higher water content and a waxy pitch-like luster.

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

A Mexican banded agate famous for tightly swirling, contorted lacy patterns in warm reds, creams, and golds.

Sandstone altered by metamorphism, with partly recrystallized quartz grains, transitional between true sandstone and quartzite.

A mica schist containing bladed blue kyanite crystals, a marker of medium- to high-grade metamorphism of aluminous rocks.