Rock & Mineral Encyclopedia

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

Tillite

A lithified glacial till, a poorly sorted rock of mixed boulders, pebbles and fine matrix that records ancient glaciations.

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

A clastic sedimentary rock made of cemented sand grains, often quartz, recording ancient beaches, deserts, and rivers.

Glacially deposited banded agates found along Lake Michigan beaches, small waterworn pebbles with concentric red and grey banding.

Glacially transported banded agates found along Lake Huron's shores, typically small, frosted pebbles with red-orange iron banding.

A foliated metamorphic rock dominated by quartz with enough mica to give it a schistose, splitting fabric.

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

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

Fine, golden, hair-like strands of basaltic volcanic glass spun from fluid lava droplets during eruptions, named for the Hawaiian volcano goddess.

Small, smooth, teardrop-shaped beads of basaltic volcanic glass formed from airborne lava droplets, often paired with Pele's hair.

A clean, mature sandstone made almost entirely of quartz grains, representing extreme weathering, sorting, and recycling of sediment.

An organic gem formed inside mollusks from layered nacre, prized for its iridescent luster and classic elegance.

A rare granitic rock containing concentric, onion-like spheres called orbicules, prized as a striking ornamental stone.

A soft, fine-grained red metamorphosed claystone, sacred to many Native American peoples and carved into ceremonial pipes.