Rock & Mineral Encyclopedia

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

Blue Sapphire

The blue gem variety of corundum, prized for its rich color, extreme hardness, and brilliance second only to diamond.

The gem variety of corundum in every color except red, most prized in velvety blue and exceptionally hard and durable.

A dark gray-to-black feldspar variety of moonstone that shows blue and white adularescent flash against a smoky body.

A plagioclase feldspar famous for labradorescence, a dramatic flash of iridescent blue, green, and gold across a dark gray stone.