Cordierite (Iolite)
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Marketed as iolite, cordierite is a magnesium iron aluminum silicate famous for exceptionally strong trichroism, appearing deep violet-blue, pale yellow, and near-colorless when viewed along its three crystallographic axes. That property earned it the old name water sapphire and a role as a navigational aid, since Vikings may have used it to locate the sun through cloud. It crystallizes in the orthorhombic system and measures 7.0 to 7.5 on the Mohs scale. The finest gem material comes from Sri Lanka, India, and Tanzania, yielding medium to dark violet-blue stones at accessible prices, so this moderately priced semi-precious gem endures as an underappreciated alternative to blue sapphire.
Physical & Optical Properties
Category
Semi-Precious Gems
Mohs Hardness
7.0 – 7.5
Specific Gravity
2.56 – 2.66
Refractive Index
1.542 – 1.578
Crystal System
Orthorhombic
Luster
Vitreous,Greasy
Cleavage
Good
Fracture
Uneven,Conchoidal
Color
various
Birefringence
0.008
Dispersion
0.017
Pleochroism
Strong trichroism: colorless to yellowish - pale blue - dark (violet)-blue
Mohs Hardness
| Mohs | Reference mineral | Cordierite (Iolite) |
|---|---|---|
| 1 | Talc | |
| 2 | Gypsum | |
| 3 | Calcite | |
| 4 | Fluorite | |
| 5 | Apatite | |
| 6 | Orthoclase | |
| 7 | Quartz | ● |
| 8 | Topaz | |
| 9 | Corundum | |
| 10 | Diamond |
Crystal System
Value & Market
Price Tier
Moderate ($50-500/ct)
Where to Buy Cordierite (Iolite)
Blue Nile
Fine jewelry retailer
James Allen
Gemstone jewelry
Brilliant Earth
Ethically sourced gems
Amazon
Wide selection
Links may earn a commission at no extra cost to you.
About Cordierite (Iolite)
堇青石（水蓝宝石）是镁铁铝硅酸盐矿物，以其极为强烈的多色性著称——沿不同晶体轴方向分别呈现出紫罗兰蓝色、近无色和黄灰色三种色调。这一特性使维京人将其用作"太阳石"导航（通过观察多色性方向确定太阳位置）。堇青石也称"水蓝宝石"，主要产自印度、斯里兰卡、坦桑尼亚和挪威。
On this page
Jewelry Use
Durability
7/10
Suitable for daily wear
Science FYI Family
Frequently Asked Questions
What is Cordierite (Iolite)?
堇青石（水蓝宝石）是镁铁铝硅酸盐矿物，以其极为强烈的多色性著称——沿不同晶体轴方向分别呈现出紫罗兰蓝色、近无色和黄灰色三种色调。这一特性使维京人将其用作"太阳石"导航（通过观察多色性方向确定太阳位置）。堇青石也称"水蓝宝石"，主要产自印度、斯里兰卡、坦桑尼亚和挪威。
What is the hardness of Cordierite (Iolite)?
Cordierite (Iolite) has a Mohs hardness of 7.0 to 7.5, making it excellent for use in jewelry.
What color is Cordierite (Iolite)?
Cordierite (Iolite) is primarily Various.
How much does Cordierite (Iolite) cost?
Cordierite (Iolite) falls into the Moderate ($50-500/ct) price range. Prices vary based on color, clarity, cut, and origin.
What is the crystal system of Cordierite (Iolite)?
Cordierite (Iolite) belongs to the Orthorhombic crystal system.