The Gemstone Encyclopedia
Discover the world's most beautiful gemstones. Properties, origins, comparisons, and expert guides — all in one place.
Today's Gemstone
Cordierite (Iolite)
Semi-Precious Gems
Iolite (cordierite) is a strongly trichroic violet-blue gem historically used by Vikings as a navigation aid. Fine material from Sri Lanka and India; an affordable sapphire alternative. Hardness 7–7.5.
Featured Gemstones
View all →Alexandrite
Hardness: 8,5
Onyx
Hardness: 6,5
Sapphire
Hardness: 9,0
Moldavite
Hardness: 5,5
Aquamarine
Hardness: 7,5
Kunzite
Hardness: 6,0
Zircon
Hardness: 7,5
Benitoite
Hardness: 6,0
Spessartine
Hardness: 7,0
Bloodstone (Heliotrope)
Hardness: 6,5
Charoite
Hardness: 5,0
Carnelian
Hardness: 6,5
Browse by Category
Browse by Color
Learn About Gemstones
From beginner basics to advanced gemology — explore our expert-written guides and interactive tools.