Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Hemimorphite
A hydrous zinc silicate, often sky-blue, that is an ore of zinc and a collectible mineral forming botryoidal crusts and crystals.
mineral
Limonite
Limonite is an amorphous brown iron oxide ore, the rust-colored material behind ochre pigments and bog iron.
mineral
Onyx
A banded variety of chalcedony quartz, classically black or black-and-white, long favored for cameos and beads.
gemstone
Black Onyx
A solid jet-black chalcedony, usually a dyed and treated agate, prized for sleek polished beads, cabochons, and intaglios.
gemstone
Onyx Marble
Translucent banded calcium-carbonate stone deposited in caves and springs, prized for ornamental carvings despite its softness.
sedimentary
Bog Iron
A soft, porous iron ore of limonite and goethite that forms in wetlands and bogs, historically the first iron source for many cultures.
sedimentary
Fire Agate
A rare brown chalcedony containing thin iron-oxide layers that produce flashing, fiery rainbow iridescence like trapped flames.
gemstone
Golden Healer Quartz
Quartz colored or coated by golden iron oxides such as limonite or goethite, giving a warm sunlit yellow glow.
crystal
Black Agate
A deep black variety of banded chalcedony, often closely related to or treated like onyx, used for jewelry and carvings.
gemstone
Sardonyx
A banded chalcedony combining reddish-brown sard with white or black onyx layers, prized since antiquity for carved cameos.
gemstone
Aquamarine Matrix
Aquamarine crystals still attached to their natural host rock, prized as mineral specimens showing beryl in its original pocket setting.
mineral
Riband Agate
A banded chalcedony with straight, ribbon-like parallel layers, often cut across the bands for striking striped cabochons.
gemstone
Green Marble
A green ornamental stone, often serpentine-rich marble or verde antique, valued for its rich green color and white veining.
metamorphic
Banded Agate
The classic agate defined by concentric or parallel bands of chalcedony in varied colors, the archetype of all agate varieties.
gemstone
Cipollino Marble
A green-and-white banded metamorphic marble whose wavy mica layers resemble the rings of a sliced onion.
metamorphic
Travertine
A banded, porous limestone deposited by mineral springs, prized as a warm-toned natural building and tile stone.
sedimentary
Goethite
Goethite is a common brown iron oxyhydroxide, the main crystalline component of limonite and rust, with shimmering botryoidal forms.
mineral
Pumice
A frothy, lightweight volcanic glass so full of gas bubbles that it can float on water.
igneous
Talc
The softest mineral on the Mohs scale, talc has a greasy, soapy feel and is the source of talcum powder and soapstone.
mineral
Chromite
Chromite is the only commercial ore of chromium, a black iron-chromium oxide of the spinel group found in mafic igneous rocks.
mineral
Contra-Luz Opal
A rare opal whose play-of-color appears only when light passes through it, glowing best when backlit or held to the light.
gemstone
Dolomite
A calcium-magnesium carbonate mineral and rock similar to limestone but harder and only weakly reactive to acid.
mineral
Bastnasite
A rare-earth fluorocarbonate that is one of the world's most important ores of cerium, lanthanum, and other rare earth elements.
mineral
Morion Quartz
The darkest, near-opaque black variety of smoky quartz, colored by natural radiation acting on trace aluminum.
crystal