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
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