Rock & Mineral Encyclopedia

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

Siltstone

A fine-grained clastic rock of silt-sized grains, intermediate between sandstone and mudstone, with a gritty feel.

A prized plume agate with rose-pink and red feathery inclusions suspended in clear chalcedony, from the western U.S.

Plume and fortification agate from the famous Woodward Ranch near Alpine, Texas, known for red and pink plumes.

A coarse, feldspar-rich sandstone, often pink, that records rapid erosion of granitic source rock under arid conditions.

Also called Sci-Fi Jasper, a Mexican jasper-rhyolite with swirling abstract patterns in cream, tan, gray, pink, and green.

A warmly colored chalcedony agate with reds, oranges, golds, and pinks that blend like the glowing bands of a sunset sky.

A fine-grained volcanic rock dominated by alkali feldspar, the extrusive equivalent of syenite.

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