Rock & Mineral Encyclopedia

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

Dendritic Opal

A common opal with branching, tree-like mineral inclusions that create natural fern, moss, or landscape patterns.

A vivid pinkish-red rhodolite garnet named for its raspberry color, a bright pyrope-almandine blend popular in jewelry.

Deeply saturated green tourmaline colored by iron, often so dark it appears nearly black until viewed in bright light.

A dark green chalcedony speckled with blood-red spots of iron oxide, traditionally known as heliotrope.

A warm orange to tangerine tourmaline, an uncommon hue produced by manganese and iron in the crystal.

A cheerful yellow opal ranging from translucent common opal to golden fire opal, colored by trace iron in the silica.

Obsidian colored brown by iron oxide inclusions, frequently banded or swirled with black as in mahogany obsidian.

A hydrous, iron-rich garnet of the hydrogarnet group in which hydroxyl groups substitute for silica within the andradite structure.

A soft, glowing orange variety of calcite colored by iron oxides, popular as tumbled stones and known for fizzing in acid.

A black titanium garnet related to andradite and schorlomite, containing tetravalent titanium and ferrous iron, found in skarns and alkaline rocks.

A translucent chalcedony decorated with branching, fern-like manganese or iron oxide inclusions resembling tiny plants.

Obsidian colored orange by iron oxide inclusions; vivid uniform orange material is frequently manufactured glass rather than volcanic.

A glacier-transported banded agate from the Lake Superior region, colored by iron into rich reds and oranges, and Minnesota's state gemstone.