Gem Structure Table
How does a gem's crystal system affect its properties? Consult our gem structure table to learn more about selected gemstones.
By International Gem Society, updated on
Many gemstone properties stem from the crystal systems in which minerals form. The following gem structure table lists selected physical and optical characteristics based on mineral crystal systems, include characteristics of non-mineral amorphous gemstones.
Crystal System | Crystal Axes and Angles | Isotropy/Anisotropy | Refractive Index | Optic Character | Pleochroism | Examples |
Amorphous | No order, no axes | Isotropic | 1 RI | None | None | Opal, Amber, Glass, Plastic |
Isometric | 1 axis length, all at 90° | Isotropic | 1 RI | None | None | Diamond, Spinel, Garnet |
Tetragonal | 2 axis lengths, all at 90° | Anisotropic | 2 RIs | Uniaxial | May be dichroic | Zircon |
Hexagonal | 2 axis lengths | Anisotropic | 2 RIs | Uniaxial | May be dichroic | Quartz, Beryl, Apatite, Corundum, Tourmaline |
Orthorhombic | 3 axis lengths, all at 90° | Anisotropic | 3 RIs | Biaxial | May be trichroic | Topaz, Zoisite, Peridot |
Monoclinic | 3 axis lengths, 2 axes at 90° (1 oblique) | Anisotropic | 3 RIs | Biaxial | May be trichroic | Orthoclase, Spodumene |
Triclinic | 3 axis lengths, all axes oblique | Anisotropic | 3 RIs | Biaxial | May be trichroic | Labradorite, Axinite |
Gem structure table, compliments of The International Gem Society.
International Gem Society
Related Articles
Table of Refractive Indices and Double Refraction of Selected Gems
Refractive indices and double refraction (birefringence) help gemologists identify gems. The following table lists these values for selected gemstones.
Read More
How to Estimate Gem Weight in a Jewelry Setting
Although you can't weigh a gemstone in a jewelry setting, you can get a close approximation of the gem weight...
Read More
Bead and Necklace Size Charts
Whether you’re a novice bead jewelry maker or just shopping for necklaces, these bead and necklace size charts and links...
Read More
Ring Size Comparison Chart
Ring Size Comparison Chart compliments of the International Gem Society. A conversion table of Ring sizes. 7 different ring size...
Read More
Latest Articles
Gemstone Radiation Treatment
Gemstone radiation is a common but little understood technique for altering colors. Learn how it works and what gems usually...
Read More
Alternative Birthstones
Not happy with your birthstone? Explore these alternative birthstones associated with astrological signs, angels, the hour or day of your...
Read More
What is Moonstone Gemstone? Value, Price, and Color
Explore moonstone’s value, meaning, and properties. Discover why this gem’s shimmering beauty makes it a top jewelry pick!
Read More
21 Beautiful Pink Gemstones: A Complete Guide
Discover 21 stunning pink gemstones , including diamond, morganite, and tourmaline. Learn hardness, rarity, and pricing for each pink gemstone...
Read More
Never Stop Learning
When you join the IGS community, you get trusted diamond & gemstone information when you need it.
Get Gemology Insights
Get started with the International Gem Society’s free guide to gemstone identification. Join our weekly newsletter & get a free copy of the Gem ID Checklist!