Rock & Mineral Encyclopedia

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

Mahogany Obsidian

A natural volcanic glass with rich brown and black mahogany-like swirls created by iron oxide inclusions.

A yellow to golden banded chalcedony colored by iron, ranging from natural honey tones to dyed commercial stones.

A banded rhyolitic volcanic rock with swirling tan, red, and yellow iron-oxide layers prized as a decorative picture stone.

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

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

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

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

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