Refractive Index Chart

Refractive index, or RI is one of the most important signatures of a gemstone. Measuring the refractive index is one of the first steps in identifying a gemstone, though some gems have similar refractive indices and additional tests are required for a definitive identification.

RI is the difference between the speed of light in a vacuum and the speed of light in the gemstone. As light passes through a gemstone, it slows down because a gemstone is denser than air. This causes the path of light to change. Refraction is the bending of light as it passes in or out of a gem. The angle of refraction in the stone determines its RI. Gemstones with a high RI are more brilliant than those with a low RI. Diamond has an RI of 2.42; quartz, has an RI of 1.54-1.55. The RI of most gems is easily measured using a simple optical instrument known as a refractometer.

Sphalerite, Diamond & Hematite - Gems with High Refractive Indices

Some gemstones are singly refractive; they have only one refractive index, but most are doubly refractive; they have two different refractive indices. When a beam of light enters a doubly refractive gem, it is split into two beams, each travelling at a different speed and on a different path through the crystal. Birefringence is a measurement of the difference between the two refractive indices in gems that are doubly refractive, and it ranges from a low of .003 to a high of .287. Very few gemstones are singly refractive; in fact, the only well-known gems with that property are diamond, spinel and garnet.

The following chart lists the refractive indices for 143 varieties of gemstones, arranged in descending order.

Hematite Refractive Index 2.94 - 3.22 Double Refraction Yes Birefringence 0.287

Diamond Refractive Index 2.417 - 2.419 Double Refraction None Birefringence NA

Sphalerite Refractive Index 2.368 - 2.371 Double Refraction None Birefringence NA

Cassiterite Refractive Index 1.997 - 2.098 Double Refraction Yes Birefringence 0.096 to 0.098

Demantoid Garnet Refractive Index 1.88 - 1.94 Double Refraction None Birefringence NA

Melanite Refractive Index 1.88 - 1.94 Double Refraction None Birefringence NA

Sphene Refractive Index 1.843 - 2.11 Double Refraction Yes Birefringence 0.100 to 0.192

Zircon Refractive Index 1.81 - 2.024 Double Refraction Yes Birefringence 0.002 to 0.059

Spessartite Garnet Refractive Index 1.79 - 1.82 Double Refraction None Birefringence NA

Almandine Garnet Refractive Index 1.77 - 1.82 Double Refraction None Birefringence NA

Ruby Refractive Index 1.762 - 1.778 Double Refraction Yes Birefringence 0.008

Star Sapphire Refractive Index 1.762 - 1.778 Double Refraction Yes Birefringence 0.008

Color Change Sapphire Refractive Index 1.762 - 1.788 Double Refraction Yes Birefringence 0.008

Star Ruby Refractive Index 1.762 - 1.778 Double Refraction Yes Birefringence 0.008

Sapphire Refractive Index 1.762 - 1.778 Double Refraction Yes Birefringence 0.008

Alexandrite Refractive Index 1.746 - 1.763 Double Refraction Yes Birefringence 0.004 to 0.010

Chrysoberyl Refractive Index 1.746 - 1.763 Double Refraction Yes Birefringence 0.007 to 0.011

Chrysoberyl Cat's Eye Refractive Index 1.746 - 1.763 Double Refraction Yes Birefringence 0.004 to 0.010

Mali Garnet Refractive Index 1.734 - 1.759 Double Refraction None Birefringence NA

Grossularite Garnet Refractive Index 1.734 - 1.759 Double Refraction None Birefringence NA

Tsavorite Garnet Refractive Index 1.734 - 1.759 Double Refraction None Birefringence NA

Color-Change Garnet Refractive Index 1.73 - 1.756 Double Refraction None Birefringence NA

Hessonite Garnet Refractive Index 1.73 - 1.75 Double Refraction None Birefringence NA

Pyrope Garnet Refractive Index 1.72 - 1.756 Double Refraction None Birefringence NA

Star Garnet Refractive Index 1.72 - 1.756 Double Refraction None Birefringence NA

Rhodolite Garnet Refractive Index 1.72 - 1.76 Double Refraction None Birefringence NA

Azurite Refractive Index 1.72 - 1.848 Double Refraction Yes Birefringence 0.108 to 0.110

Rhodonite Refractive Index 1.716 - 1.752 Double Refraction Yes Birefringence 0.010 to 0.014

Spinel Refractive Index 1.712 - 1.762 Double Refraction None Birefringence NA

Kyanite Refractive Index 1.71 - 1.734 Double Refraction Yes Birefringence 0.0015 to 0.033

Color Change Diaspore Refractive Index 1.702 - 1.75 Double Refraction Yes Birefringence 0.048

Cat's Eye Diaspore Gems Refractive Index 1.702 - 1.75 Double Refraction Yes Birefringence 0.048

Idocrase Refractive Index 1.7 - 1.723 Double Refraction Yes Birefringence 0.002 to 0.012

Ruby-Zoisite Refractive Index 1.691 - 1.7 Double Refraction Yes Birefringence 0.009

Tanzanite Refractive Index 1.691 - 1.7 Double Refraction Yes Birefringence 0.009

Dumortierite Quartz Refractive Index 1.678 - 1.689 Double Refraction Yes Birefringence 0.015 to 0.037

Tashmarine Diopside Refractive Index 1.664 - 1.73 Double Refraction Yes Birefringence 0.024 to 0.031

Star Diopside Refractive Index 1.664 - 1.73 Double Refraction Yes Birefringence 0.024 to 0.031

Chrome Diopside Refractive Index 1.664 - 1.73 Double Refraction Yes Birefringence 0.024 to 0.031

Spodumene Refractive Index 1.66 - 1.681 Double Refraction Yes Birefringence 0.014 to 0.016

Kunzite Refractive Index 1.66 - 1.681 Double Refraction Yes Birefringence 0.014 to 0.016

Hiddenite Refractive Index 1.66 - 1.681 Double Refraction Yes Birefringence 0.014 to 0.016

Axinite Refractive Index 1.656 - 1.704 Double Refraction Yes Birefringence 0.010 to 0.012

Sillimanite Cat's Eye Refractive Index 1.655 - 1.684 Double Refraction Yes Birefringence 0.014 to 0.021

Malachite Refractive Index 1.655 - 1.909 Double Refraction Yes Birefringence 0.254

Peridot Refractive Index 1.65 - 1.703 Double Refraction Yes Birefringence 0.036 to 0.038

Danburite Refractive Index 1.63 - 1.636 Double Refraction Yes Birefringence 0.006 to 0.008

Clinohumite Refractive Index 1.629 - 1.674 Double Refraction Yes Birefringence 0.029 - 0.045

Cat's Eye Apatite Refractive Index 1.628 - 1.649 Double Refraction Yes Birefringence 0.002 to 0.006

Apatite Refractive Index 1.628 - 1.649 Double Refraction Yes Birefringence 0.002 to 0.006

Andalusite Refractive Index 1.627 - 1.649 Double Refraction Yes Birefringence 0.007 to 0.013

Smithsonite Refractive Index 1.621 - 1.849 Double Refraction Yes Birefringence 0.228

Cat's Eye Tourmaline Refractive Index 1.614 - 1.666 Double Refraction Yes Birefringence 0.014 to 0.032

Tourmaline Refractive Index 1.614 - 1.666 Double Refraction Yes Birefringence 0.014 to 0.032

Rubellite Tourmaline Refractive Index 1.614 - 1.666 Double Refraction Yes Birefringence 0.014 to 0.032

Chrome Tourmaline Refractive Index 1.614 - 1.666 Double Refraction Yes Birefringence 0.014 to 0.032

Paraiba Tourmaline Refractive Index 1.614 - 1.666 Double Refraction Yes Birefringence 0.014 to 0.032

Hemimorphite Refractive Index 1.614 - 1.636 Double Refraction Yes Birefringence 0.022

Prehnite Refractive Index 1.611 - 1.669 Double Refraction Yes Birefringence 0.0021 to 0.039

Turquoise Refractive Index 1.61 - 1.65 Double Refraction Yes Birefringence 0.040

Gaspeite Refractive Index 1.61 - 1.81 Double Refraction Yes Birefringence 0.22

Imperial Topaz Refractive Index 1.609 - 1.643 Double Refraction Yes Birefringence 0.008 to 0.016

Rutile Topaz Refractive Index 1.609 - 1.643 Double Refraction Yes Birefringence 0.008 to 0.016

Mystic Topaz Refractive Index 1.609 - 1.643 Double Refraction Yes Birefringence 0.008 to 0.016

Azotic Topaz Refractive Index 1.609 - 1.643 Double Refraction Yes Birefringence 0.008 to 0.016

Topaz Refractive Index 1.609 - 1.643 Double Refraction Yes Birefringence 0.008 to 0.016

Sugilite Refractive Index 1.607 - 1.611 Double Refraction Yes Birefringence 0.001 to 0.004

Jadeite Refractive Index 1.6 - 1.627 Double Refraction Yes Birefringence 0.027

Nephrite Jade Refractive Index 1.6 - 1.627 Double Refraction Yes Birefringence 0.027

Rhodochrosite Refractive Index 1.6 - 1.82 Double Refraction Yes Birefringence 0.208 to 0.220

Larimar Refractive Index 1.595 - 1.645 Double Refraction Yes Birefringence 0.038

Howlite Refractive Index 1.586 - 1.605 Double Refraction Yes Birefringence 0.019

Seraphinite Refractive Index 1.576 - 1.599 Double Refraction Yes Birefringence 0.005 to 0.011

Emerald Refractive Index 1.565 - 1.602 Double Refraction Yes Birefringence 0.006

Cat's Eye Aquamarine Refractive Index 1.564 - 1.596 Double Refraction Yes Birefringence 0.004 to 0.005

Aquamarine Refractive Index 1.564 - 1.596 Double Refraction Yes Birefringence 0.004 to 0.005

Variscite Refractive Index 1.563 - 1.594 Double Refraction Yes Birefringence 0.031

Beryl Refractive Index 1.562 - 1.602 Double Refraction Yes Birefringence 0.004 to 0.010

Goshenite Refractive Index 1.562 - 1.602 Double Refraction Yes Birefringence 0.004 to 0.010

Morganite Refractive Index 1.562 - 1.602 Double Refraction Yes Birefringence 0.004 to 0.010

Serpentine Refractive Index 1.56 - 1.571 Double Refraction Yes Birefringence 0.008 to 0.014

Labradorite Refractive Index 1.559 - 1.57 Double Refraction Yes Birefringence 0.008 to 0.010

Hambergite Refractive Index 1.553 - 1.628 Double Refraction Yes Birefringence 0.0072

Verdite Refractive Index 1.552 - 1.576 Double Refraction None Birefringence NA

Andesine Labradorite Refractive Index 1.551 - 1.561 Double Refraction Yes Birefringence 0.008

Charoite Refractive Index 1.55 - 1.561 Double Refraction Yes Birefringence 0.004 to 0.009

Citrine Refractive Index 1.544 - 1.553 Double Refraction Yes Birefringence 0.009

Rose Quartz Refractive Index 1.544 - 1.553 Double Refraction Yes Birefringence 0.009

Pietersite Refractive Index 1.544 - 1.553 Double Refraction Yes Birefringence 0.009

Amethyst Refractive Index 1.544 - 1.553 Double Refraction Yes Birefringence 0.009

Onyx Refractive Index 1.544 - 1.553 Double Refraction Yes Birefringence up to 0.004

Mystic Quartz Refractive Index 1.544 - 1.553 Double Refraction Yes Birefringence 0.009

Quartz Refractive Index 1.544 - 1.553 Double Refraction Yes Birefringence 0.009

Strawberry Quartz Refractive Index 1.544 - 1.553 Double Refraction Yes Birefringence 0.009

Smoky Quartz Refractive Index 1.544 - 1.553 Double Refraction Yes Birefringence 0.009

Ametrine Refractive Index 1.544 - 1.553 Double Refraction Yes Birefringence 0.009

Rutile Quartz Refractive Index 1.544 - 1.553 Double Refraction Yes Birefringence 0.009

Aventurine Refractive Index 1.544 - 1.553 Double Refraction Yes Birefringence 0.009

Iolite Refractive Index 1.542 - 1.578 Double Refraction Yes Birefringence 0.008 to 0.012

Jasper Refractive Index 1.54 Double Refraction None Birefringence NA

Peanut Wood Refractive Index 1.54 Double Refraction None Birefringence NA

Cat's Eye Scapolite Refractive Index 1.54 - 1.579 Double Refraction Yes Birefringence 0.006 to 0.037

Scapolite Refractive Index 1.54 - 1.579 Double Refraction Yes Birefringence 0.006 to 0.037

Amber Refractive Index 1.539 - 1.545 Double Refraction None Birefringence NA

Tiger's Eye Matrix Refractive Index 1.534 - 1.54 Double Refraction None Birefringence NA

Quartz Cat's Eye Refractive Index 1.534 - 1.54 Double Refraction None Birefringence NA

Tiger's Eye Refractive Index 1.534 - 1.54 Double Refraction None Birefringence NA

Fire Agate Refractive Index 1.53 - 1.54 Double Refraction Yes Birefringence up to 0.004

Chrysoprase Refractive Index 1.53 - 1.54 Double Refraction Yes Birefringence 0.004 to 0.009

Carnelian Refractive Index 1.53 - 1.54 Double Refraction Yes Birefringence up to 0.004

Agate Geode Refractive Index 1.53 - 1.54 Double Refraction Yes Birefringence up to 0.004

Bloodstone Refractive Index 1.53 - 1.54 Double Refraction Yes Birefringence up to 0.004

Chalcedony Refractive Index 1.53 - 1.54 Double Refraction Yes Birefringence up to 0.004

Star Rose Quartz Refractive Index 1.53 - 1.54 Double Refraction Yes Birefringence 0.009

Fossil Coral Refractive Index 1.53 - 1.54 Double Refraction Yes Birefringence up to 0.004

Dendritic Agate Refractive Index 1.53 - 1.54 Double Refraction Yes Birefringence up to 0.004

Agate Refractive Index 1.53 - 1.54 Double Refraction Yes Birefringence up to 0.004

Star Sunstone Refractive Index 1.525 - 1.548 Double Refraction Yes Birefringence 0.010

Sunstone Refractive Index 1.525 - 1.548 Double Refraction Yes Birefringence 0.010

Lepidolite Refractive Index 1.525 - 1.586 Double Refraction Yes Birefringence 0.0290 to 0.0380

Amazonite Refractive Index 1.522 - 1.53 Double Refraction Yes Birefringence 0.008

Maw-Sit-Sit Refractive Index 1.52 - 1.74 Double Refraction Yes Birefringence 0.0150 to 0.020

Pearl Refractive Index 1.52 - 1.69 Double Refraction Yes Birefringence 0.156

Ammolite Refractive Index 1.52 - 1.68 Double Refraction Yes Birefringence 0.155

Star Moonstone Refractive Index 1.518 - 1.526 Double Refraction Yes Birefringence 0.008

Moonstone Refractive Index 1.518 - 1.526 Double Refraction Yes Birefringence 0.008

Rainbow Moonstone Refractive Index 1.518 - 1.526 Double Refraction Yes Birefringence 0.008

Orthoclase Refractive Index 1.518 - 1.53 Double Refraction Yes Birefringence 0.008

Lapis Lazuli Refractive Index 1.5 Double Refraction None Birefringence NA

Coral Refractive Index 1.486 - 1.658 Double Refraction Yes Birefringence White and red: 0.160 to 0.172

Calcite Refractive Index 1.486 - 1.658 Double Refraction Yes Birefringence 0.172

Hackmanite Refractive Index 1.48 Double Refraction None Birefringence NA

Sodalite Refractive Index 1.48 Double Refraction None Birefringence NA

Moldavite Refractive Index 1.48 - 1.54 Double Refraction None Birefringence NA

Chrysocolla Refractive Index 1.469 - 1.57 Double Refraction Yes Birefringence 0.023 to 0.040

Snowflake Obsidian Refractive Index 1.45 - 1.55 Double Refraction None Birefringence NA

Obsidian Refractive Index 1.45 - 1.55 Double Refraction None Birefringence NA

Fluorite Refractive Index 1.434 Double Refraction None Birefringence NA

Fire Opal Refractive Index 1.37 - 1.52 Double Refraction None Birefringence NA

Boulder Opal Refractive Index 1.37 - 1.52 Double Refraction None Birefringence NA

Opal Doublet Refractive Index 1.37 - 1.52 Double Refraction None Birefringence NA

Opal Refractive Index 1.37 - 1.52 Double Refraction None Birefringence NA