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Refractive Index (RI) of Gems

Click HERE for the Refractive Index (RI) list.

 

Refractive Index (RI) is the characteristic slowing of light as it travels through a given gem species or substance. The higher the RI, the greater brilliance and luster is possible. The fact that each gem has its own RI makes it necessary to facet each species at slightly different angles and makes it a useful characteristic in gem identification.

What is the Index of Refraction?
Light moves at its maximum possible velocity in the absence of matter. For example, in space light travels approximately 186,000 miles per second. But the presence of matter slows light down; or more specifically, the forces which bind atoms slow light down. The Index of Refraction for any substance is the ratio of the velocity of light in a vacuum to its velocity in a given substance. The higher the index, the slower the velocity. Thus, if we say that a particular crystal has an index of refraction of 2.000 we mean that light would pass through a vacuum at twice the velocity that it can go through that crystal.

Why do different substances have different refractive indices?
As previously pointed out, the velocity of light through any material is retarded by forces binding its atoms and molecules. Therefore, the degree to which a particular beam of light is slowed depends both upon the types of atoms present (the chemical composition) and the nature of the arrangement of those atoms.

For example, light travels in water at 3/4 of its velocity in a vacuum, so we assign a value of 4/3, or 1.333 as the index of refraction of water. But if we freeze that water into ice, a different arrangement of the molecules results and the ice has a refractive index of 1.313. Or, if we boil the water, yet another arrangement of the same molecules is produced, which retards the light very little, and the steam has a refractive index of 1.0002.

In the case of ice, water and steam, we have examples of three different states of matter; solid, liquid and gas. But, even when a single state of matter is considered, it must be remembered that the identical materials can often be arranged in different structures, which are reflected in the differing indices of refraction.

For example, common pure Quartz crystals have an average index of 1.548. But if the crystal is melted and then cooled down to room temperature, the resulting fused silica-quartz has an index of 1.456. Or the same silicon dioxide may also exist as tridymite, cristobalite, coesite or other differing crystal structures, each of which has a different refractive index, although all have the identical chemical composition.

Does light always travel through a given crystal at the same speed?
No. Most minerals crystallize in an orderly lattice work that has different types of inter-molecular bonds in different planes, much like the grain in wood. The strength of these bonds may be very different in different planes.

The form of Calcite known as Iceland Spar presents an outstanding example of the effect on refractive index in different optical directions, since a given crystal will have an index of 1.486 in one direction and 1.658 in another. Fortunately (except for Rutile) most minerals used as gems do not vary so widely in different directions.

What other factors affect the Refractive Index of a mineral?
Temperature of the specimen influences its index, but if measurements are made at a normal range of room temperatures, this effect is so small that it can be neglected.

Impurities in the specimen have an effect proportionate to their concentration in the specimen. For example, Opal consists mainly of a form of silica known as cristobalite with an index of 1.487. But Opal usually contains about 5 to 10% of water in its structure. Since water has an index of 1.33, Opals show an index somewhere between those two values, usually 1.43 to 1.46.  

 

 

Refractive Index of Gems

 

 

 

 

A
 

RI values

Birefringence

Optics

 

 

Achroite (Tourmaline)

1.614 - 1.666

0.014 - 0.040

Uniaxial (-)

 

 

Acmite (Aegirine)

1.720 - 1.839

0.037 - 0.061

Biaxial (-)

 

 

Actinolite

1.613 - 1.666

0.023

Biaxial (-)

 

 

Adamite

1.708 - 1.773

0.055

Biaxial (+/-)

 

 

Adularia (Microcline)

1.514 - 1.539

0.007 - 0.010

Biaxial (-)

 

 

Adventurine (Quartz)

1.543 - 1.554

0.009

Uniaxial (+)

 

 

Aegirine

1.720 - 1.839

0.037-0.061

Biaxial (-)

 

 

Aenigmatite

1.780 - 1.900

0.090 - 0.100

Biaxial (+)

 

 

Aerinite

1.510 - 1.580

0.070

Biaxial (-)

 

 

Aeschynite-(Y)

2.190 - 2.500

0.150 - 0.220

Biaxial (+)

 

 

Afghanite

1.523 - 1.529

0.006

Uniaxial (+)

 

 

Agate (Quartz)

1.543 - 1.554

0.009

Uniaxial (+)

 

 

Agrellite

1.567 - 1.581

0.014

Biaxial (-)

 

 

Ajoite

1.550 - 1.641

0.091

Biaxial (+)

 

 

Alabandite

2.700

0 (Isotropic)

Isotropic

 

 

Albite (Feldspar)

1.528 - 1.542

0.010

Biaxial (+)

 

 

Alexandrite (Chrysoberyl)

1.746 - 1.756

0.010

Biaxial (+)

 

 

Allanite-(Ce)

1.715 - 1.822

0.018 - 0.031

Biaxial (-)

 

 

Allanite-(La)

1.755 - 1.765

0.010

Biaxial (-)

 

 

Almandine (Garnet)

1.830

0 (Isotropic)

Isotropic

 

 

Alum-(K)

1.453

0 (Isotropic)

Isotropic

 

 

Alunite

1.572 - 1.592

0.020

Uniaxial (+)

 

 

Alurgite (Muscovite)

1.552 - 1.618

0.035 - 0.042

Biaxial

 

 

Amazonite (Feldspar)

1.514 - 1.539

0.007 - 0.010

Biaxial (-)

 

 

Amber

1.539 - 1.545

0 (Isotropic)

Isotropic

 

 

Amblygonite

1.577 - 1.613

0.019 - 0.022

Biaxial (-)

 

 

Amesite

1.597 - 1.615

0.015 - 0.018

Biaxial (+)

 

 

Amethyst (Quartz)

1.543 - 1.554

0.009

Uniaxial (+)

 

 

Ametrine (Quartz)

1.543 - 1.554

0.009

Uniaxial (+)

 

 

Analcime

1.479 - 1.494

0.001

Biaxial (-)

 

 

Anapaite

1.602 - 1.649

0.037 - 0.047

Biaxial (+)

 

 

Anatase

2.488 - 2.561

0.073

Uniaxial (-)

 

 

Andalusite

1.629 - 1.650

0.009 - 0.010

Biaxial (-)

 

 

Andesine (Albite, Feldspar)

1.528 - 1.542

0.010

Biaxial (+)

 

 

Andradite (Garnet)

1.887

0 (Isotropic)

Isotropic

 

 

Angelite (Anhydrite)

1.567 - 1.618

0.042 - 0.044

Biaxial (+)

 

 

Anglesite

1.878 - 1.895

0.017

Biaxial (+)

 

 

Anhydrite

1.567 - 1.618

0.042 - 0.044

Biaxial (+)

 

 

Annabergite

1.622 - 1.687

0.065

Biaxial (+/-)

 

 

Anorthite (Feldspar)

1.573 - 1.590

0.012 - 0.013

Biaxial (-)

 

 

Anthophyllite

1.598 - 1.697

0.017 - 0.023

Biaxial (+)

 

 

Antigorite

1.555 - 1.573

0.005 - 0.006

Biaxial (-)

 

 

Apache Tears (Obsidian)

1.450 - 1.550

0 (Isotropic)

Isotropic

 

 

Apatite (Fluorapatite)

1.631 - 1.646

0.004

Uniaxial (-)

 

 

Apophyllite

1.530 - 1.538

0.002

Uniaxial (+)

 

 

Aquamarine (Beryl)

1.568 - 1.595

0.004 - 0.007

Uniaxial (-)

 

 

Aragonite

1.529 - 1.686

0.156

Biaxial (-)

 

 

Arfvedsonite

1.652 - 1.708

0.014

Biaxial (-)

 

 

Arrojadite-(KFe)

1.664 - 1.675

0.011

Biaxial (+)

 

 

Artinite

1.488 - 1.557

0.068

Biaxial (-)

 

 

Ascharite (Szaibelyite)

1.530 - 1.740

0.020 - 0.070

Biaxial (-)

 

 

Astrophyllite

1.680 - 1.730

0.050

Biaxial (+)

 

 

Augelite

1.574 - 1.588

0.014 - 0.015

Biaxial (+)

 

 

Augite

1.680 - 1.774

0.026 - 0.039

Biaxial (+)

 

 

Aurichalcite

1.655 - 1.744

0.089

Biaxial (-)

 

 

Austinite

1.759(3) - 1.783(3)

0.024

Biaxial (+)

 

 

Autunite

1.584 - 1.607

0.015 - 0.023

Uniaxial (-)

 

 

Axinite-(Fe)

1.672 - 1.704

0.009 - 0.011

Biaxial (-)

 

 

Axinite-(Mg)

1.672 - 1.704

0.009 - 0.011

Biaxial (-)

 

 

Azurite

1.730 - 1.838

0.108

Biaxial (+)

 

 

 

 

 

 

 

B
 

RI values

Birefringence

Optics

 

 

Babingtonite

1.700 - 1.725

0.025

Biaxial (-)

 

 

Baddeleyite

2.130 - 2.200

0.070

Biaxial (-)

 

 

Bahianite

1.810 - 1.920

0.110

Biaxial (-)

 

 

Bakerite

1.624 - 1.654

0.030

Biaxial (-)

 

 

Baratovite

1.666 - 1.674

0.008

Biaxial (+)

 

 

Barite (Baryte)

1.636 - 1.648

0.012

Biaxial (+)

 

 

Barkevikite (Ferro-edenite)

1.710 - 1.730

0.020

Biaxial (-)

 

 

Barrerite

1.479 - 1.489

0.010

Biaxial (-)

 

 

Bastnäsite-(Ce)

1.717 - 1.823

0.101

Uniaxial (+)

 

 

Bementite

1.602 - 1.650

0.028 - 0.030

Biaxial

 

 

Benitoite

1.756 - 1.804

0.046

Uniaxial (+)

 

 

Bertossaite

1.624 - 1.642

0.018

Biaxial (-)

 

 

Bertrandite

1.591 - 1.614

0.023

Biaxial (-)

 

 

Beryl Group

1.568 - 1.602

0.004 - 0.007

Uniaxial (-)

 

 

Beryllonite

1.552 - 1.561

0.009

Biaxial (-)

 

 

Betafite

1.910 - 2.197

0 (Isotropic)

Isotropic

 

 

Binghamite (Chalcedony)

1.543 - 1.554

0.009

Uniaxial (+)

 

 

Bisbeeite (Chrysocolla)

1.575 - 1.635

0.023 - 0.050

Biaxial (-)

 

 

Bixbite (Beryl)

1.568 - 1.595

0.004 - 0.007

Uniaxial (-)

 

 

Blödite

1.483 - 1.487

0.004

Biaxial (-)

 

 

Bloodstone (Chalcedony)

1.543 - 1.554

0.009

Uniaxial (+)

 

 

Boleite

2.050

0 (Isotropic)

Isotropic

 

 

Boracite

1.658 - 1.673

0.010 - 0.011

Biaxial (+)

 

 

Bowenite (Antigorite)

1.555 - 1.573

0.005 - 0.006

Biaxial (-)

 

 

Brazilianite

1.602 - 1.623

0.019 - 0.021

Biaxial (+)

 

 

Brochantite

1.728 - 1.800

0.072

Biaxial (-)

 

 

Bromellite

1.705 - 1.733

0.028

Uniaxial (+)

 

 

Brookite

2.583 - 2.700

0.117 - 0.1173

Biaxial (+)

 

 

Bronzite (Enstatite)

1.650 - 1.679

0.009 - 0.011

Biaxial (+)

 

 

Brucite

1.560 - 1.600

0.020

Biaxial (+)

 

 

Burangaite

1.611 - 1.643

0.032

Biaxial (-)

 

 

Burbankite

1.616 - 1.623

0.019

Uniaxial (-)

 

 

Burmite (Amber)

1.539 - 1.545

0 (Isotropic)

Isotropic

 

 

Buserite

1.690 - 1.730

0.040

Uniaxial (-)

 

 

Bustamite

1.640 - 1.710

0.013 - 0.015

Biaxial (-)

 

 

Bytownite

1.563 - 1.583

0.010 - 0.011

Biaxial (+/-)

 

 

 

 

 

 

 

 

C
 

RI values

Birefringence

Optics

 

 

Cacoxenite

1.575 - 1.656

0.060

Uniaxial (+)

 

 

Calcite

1.486 - 1.660

0.154 - 0.174

Uniaxial (-)

 

 

Californite (Vesuvianite)

1.700 - 1.752

0.003 - 0.006

Uniaxial (+/-)

 

 

Canasite

1.534 - 1.543

0.009

Biaxial (-)

 

 

Cancrinite

1.495 - 1.528

0.012 - 0.025

Uniaxial (+/-)

 

 

Carnegieite

1.526 - 1.546

0.003 - 0.004

Uniaxial (-)

 

 

Carnelian (Chalcedony)

1.530 - 1.543

0.003 - 0.009

Uniaxial (+)

 

 

Cassiterite

1.990 - 2.100

0.103

Uniaxial (+)

 

 

Catapleiite

1.591 - 1.627

0.036

Biaxial (+)

 

 

Cavansite

1.542(2) - 1.551(2)

0.009

Biaxial (+)

 

 

Celadonite

1.579 - 1.661

0.027 - 0.030

Biaxial (-)

 

 

Celestine (Celestite)

1.619 - 1.632

0.011

Biaxial (+)

 

 

Ceruleite

1.600 - 1.620

0.020

Biaxial (?)

 

 

Cerussite

1.803 - 2.076

0.273

Biaxial (-)

 

 

Cervantite

2.000 - 2.100

0.100

Biaxial

 

 

Chabazite

1.478 - 1.493

0.002 - 0.006

Biaxial (+/-)

 

 

Chalcanthite

1.514 - 1.543

0.029

Biaxial (-)

 

 

Chalcedony

1.530 - 1.543

0.003 - 0.009

Uniaxial (+)

 

 

Chalcosiderite

1.775 - 1.844

0.069

Biaxial (-)

 

 

Chambersite

1.575 - 1.584

0.009

Biaxial (+)

 

 

Chamosite

1.600 - 1.670

0.070

Biaxial (-)

 

 

Charlesite

1.492 - 1.475

0.017

Uniaxial (-)

 

 

Charoite

1.550 - 1.559

0.009

Biaxial (+)

 

 

Chessylite (Azurite)

1.730 - 1.838

0.108

Biaxial (+)

 

 

Chevkinite-(Ce)

1.967 - 2.050

0.083

Biaxial (-)

 

 

Childrenite

1.644 - 1.691

0.027 - 0.042

Biaxial (-)

 

 

Chiastolite

1.627 - 1.645

0.007 - 0.013

Biaxial (-)

 

 

Chiquitanita (Chalcedony)

1.530 - 1.543

0.003 - 0.009

Uniaxial (+)

 

 

Chkalovite

1.544 - 1.549

0.005

Biaxial (+)

 

 

Chlorastrolite

1.674 - 1.764

0.014 - 0.016

Biaxial (+)

 

 

Chlorite (Chlinochlore)

1.571 - 1.599

0.005 - 0.011

Biaxial (+)

 

 

Chondrodite

1.592 - 1.675

0.027 - 0.032

Biaxial (+)

 

 

Chrome Diopside

1.668 - 1.703

0.024 - 0.030

Biaxial (+)

 
 

Chrome Tremolite

1.599 - 1.637

0.023 - 0.028

Biaxial (-)

 

 

Chromite

2.080 - 2.016

0 (Isotropic)

Isotropic

 

 

Chrysoberyl

1.746 - 1.756

0.010

Biaxial (+)

 

 

Chrysocolla

1.575 - 1.635

0.023 - 0.050

Biaxial (-)

 

 

Chrysoprase

1.530 - 1.543

0.004

Biaxial (+)

 

 

Chrysotile

1.569 - 1.570

0.001

Biaxial

 

 

Cinnabar

2.905 - 3.256

0.351

Uniaxial (+)

 

 

Citrine (Quartz)

1.543 - 1.554

0.009

Uniaxial (+)

 

 

Cleavelandite (Albite)

1.528 - 1.542

0.010

Biaxial (+)

 

 

Cleiophane (Sphalerite)

2.369

0 (Isotropic)

Isotropic

 

 

Clinochlore

1.571 - 1.599

0.005 - 0.011

Biaxial (+)

 

 

Clinohumite

1.623 - 1.728

0.028

Biaxial (+)

 

 

Clinozoisite

1.706 - 1.735

0.006 - 0.011

Biaxial (+)

 

 

Cobaltocalcite

1.855 - 1.600

0.255

Uniaxial (-)

 

 

Coffinite

1.730 - 1.750

1.730

Uniaxial (+/-)

 

 

Colemanite

1.586 - 1.614

0.028

Biaxial (+)

 

 

Conichalcite

1.778 - 1.846

0.023 - 0.046

Biaxial (+/-)

 

 

Connellite

1.724 - 1.758

0.014 - 0.026

Uniaxial (+)

 

 

Cookeite

1.572 - 1.600

0.017 - 0.024

Biaxial (+)

 

 

Coquimbite

1.539 - 1.548

0.009

Uniaxial (+)

 

 

Cordierite (Iolite)

1.527 - 1.578

0.011 - 0.018

Biaxial (-)

 

 

Cornetite

1.765 - 1.820

0.055

Biaxial (-)

 

 

Covellite

1.450 - 2.620

1.170

Uniaxial (+)

 

 

Crandallite

1.613 - 1.632

0.009 - 0.011

Uniaxial (+)

 

 

Creedite

1.461 - 1.485

0.024

Biaxial (-)

 

 

Cristobalite

1.478 - 1.484

0.003

Uniaxial (-)

 

 

Crocidolite (Riebeckite)

1.461 - 1.485

0.024

Biaxial (-)

 

 

Crocoite

2.290(2) - 2.660(2)

0.370

Biaxial (+)

 

 

Cryolite

1.339 - 1.340

0.001

Biaxial (-)

 

 

Cuprite

2.849

0 (Isotropic)

Isotropic

 

 

Cuproadamite

1.708 - 1.773

0.055

Biaxial (+/-)

 

 

Cuprosklodowskite

1.654 - 1.667

0.010 - 0.012

Biaxial (-)

 

 

Cyanotrichite

1.588 - 1.655

0.067

Biaxial (+)

 

 

Cymrite

1.611 - 1.621

0.010

Biaxial (-)

 

 

Cyprine (Vesuvianite)

1.703 - 1.752

0.003 - 0.006

Uniaxial (+/-)

 

 

 

 

 

 

 

 

D
 

RI values

Birefringence

Optics

 

 

Danalite

1.747 - 1.771

0 (Isotropic)

Isotropic

 

 

Danburite

1.627 - 1.639

0.006

Biaxial (+/-)

 

 

Datolite

1.626 - 1.670

0.044

Biaxial (-)

 

 

Demantoid

1.880 - 1.890

0 (Isotropic)

Isotropic

 

 

Descloizite

2.185 - 2.350

0.165

Biaxial (-)

 

 

Diaboleite

1.850 - 1.980

0.130

Uniaxial (-)

 

 

Diamond

2.435

0 (Isotropic)

Isotropic

 

 

Diaspore 

1.682 - 1.752

0.048

Biaxial (+)

 

 

Diopside

1.663 - 1.728

0.030

Biaxial (+)

 

 

Dioptase

1.652 - 1.710

0.052

Uniaxial (+)

 

 

Dolomite

1.679 - 1.503

0.179

Uniaxial (-)

 

 

Dravite (Tourmaline)

1.612 - 1.661

0.022 - 0.029

Uniaxial (-)

 

 

Dumortierite

1.659 - 1.692

0.027

Biaxial (-)

 

 

Dunilite (Olivine)

1.650 - 1.710

0.035 - 0.038

Biaxial (+)

 

 

Durangite

1.659 - 1.692

0.027

Biaxial (-)

 

 

 

 

 

 

 

E
 

RI values

Birefringence

Optics

 

 

Eitelite

1.450 - 1.605

0.155

Uniaxial (-)

 

 

Ekanite 

1.568 - 1.580

0.012

Uniaxial (-)

 

 

Elbaite (Tourmaline)

1.615 - 1.651

0.018 - 0.021

Uniaxial (-)

 

 

Emerald (Beryl)

1.565 - 1.602

0.004 - 0.010

Uniaxial (-)

 

 

Endlichite (Vanadinite)

2.350 - 2.416

0.066

Uniaxial (-)

 

 

Enstatite

1.650 - 1.679

0.009 - 0.011

Biaxial (+)

 

 

Eosphorite

1.628 - 1.679

0.029 - 0.035

Biaxial (-)

 

 

Epididymite

1.544 - 1.546

0.002

Biaxial (+)

 

 

Epidote

1.715 - 1.797

0.019 - 0.046

Biaxial (-)

 

 

Epistilbite

1.502 - 1.512

0.010

Biaxial (-)

 

 

Erythrite

1.626 - 1.701

0.073

Biaxial (+)

 

 

Esperite

1.762 - 1.774

0.012

Biaxial (-)

 

 

Ettringite

1.470 - 1.491

0.021

Uniaxial (-)

 

 

Euclase

1.652 - 1.671

0.019

Biaxial (+)

 

 

Eucryptite

1.570 - 1.587

0.013

Uniaxial (+)

 

 

Eudialyte

1.606 - 1.613

0.004

Uniaxial (+/-)

 

 

Euxenite-(Y)

2.060 - 2.240

0 (Isotropic)

Isotropic

 

 

 

 

 

 

 

F
 

RI values

Birefringence

Optics

 

 

Fassaite (Augite)

1.680 - 1.774

0.026 - 0.039

Biaxial (+)

 

 

Faustite

1.612

0

Biaxial (+)

 

 

Fayalite

1.731 - 1.875

0.042 - 0.051

Biaxial (-)

 

 

Ferberite

2.255 - 2.414

0.159

Biaxial (+)

 
 

Feldspar: Adularia

1.514 - 1.539

0.007 - 0.010

Biaxial (-)

 
 

Feldspar: Albite

1.528 - 1.542

0.010

Biaxial (+)

 
 

Feldspar: Andesine

1.528 - 1.542

0.010

Biaxial (+)

 
 

Feldspar: Anorthite

1.573 - 1.590

0.012 - 0.013

Biaxial (-)

 
 

Feldspar: Bytownite

1.563 - 1.583

0.010 - 0.011

Biaxial (+/-)

 
 

Feldspar: Hyalophane

1.542 - 1.547

0.005

Biaxial (-)

 
 

Feldspar: Labradorite

1.554 - 1.573

0.008 - 0.010

Biaxial (+)

 
 

Feldspar: Microcline

1.514 - 1.539

0.007 - 0.010

Biaxial (-)

 
 

Feldspar: Moonstone

1.518 - 1.527

0.006 - 0.007

Biaxial (-)

 
 

Feldspar: Oligoclase

1.538 - 1.550

0.010

Biaxial (-)

 
 

Feldspar: Orthoclase

1.518 - 1.525

0.004 - 0.005

Biaxial (-)

 
 

Feldspar: Sanidine

1.518 - 1.531

0.007

Biaxial (-)

 
 

Feldspar: Sunstone

1.525 - 1.552

0.007 - 0.010

Biaxial (-)

 
 

Feldspar: Valencianite

1.514 - 1.539

0.007 - 0.010

Biaxial (-)

 

 

Fergusonite-(Ce)

2.200 - 2.300

0.100

Uniaxial (-)

 

 

Ferri-Katophorite

1.640 - 1.692

0.020

Biaxial (-)

 

 

Ferro-Axinite

1.672 - 1.704

0.009 - 0.011

Biaxial (-)

 

 

Ferro-edenite

1.710 - 1.730

0.020

Biaxial (-)

 

 

Ferrotantalite

2.260 - 2.430

0.170

Biaxial (-)

 

 

Fluorapatite (Apatite)

1.631 - 1.646

0.004

Uniaxial (-)

 

 

Fluorbritholite-(Ce)

1.786 - 1.792

0.006

Uniaxial (-)

 

 

Fluorite 

1.433 - 1.448

0 (Isotropic)

Isotropic

 

 

Fluornatromicrolite 

2.030

0 (Isotropic)

Isotropic

 

 

Fluoro-potassic-hastingsite

1.668 - 1.698

0.030

Biaxial (-)

 

 

Forsterite

1.636 - 1.772

0.033 - 0.042

Biaxial (+)

 

 

Francevillite

1.752 - 2.002

0.195 - 0.217

Biaxial (-)

 

 

Franklinite

2.360(2)

0 (Isotropic)

Isotropic

 

 

Friedelite 

1.627 - 1.663

0.032 - 0.035

Uniaxial (-)

 

 

Fuchsite (Muscovite)

1.552 - 1.618

0.035 - 0.042

Biaxial (-)

 

 

 

 

 

 

 

G
 

RI values

Birefringence

Optics

 

 

Gadolinite-(Y)

1.770 - 1.820

0.050

Biaxial (+)

 

 

Gahnite

1.790 - 1.818

0 (Isotropic)

Isotropic

 

 

Ganophyllite

1.537 - 1.613

0.076

Biaxial (-)

 

 

Garnet: Almandine

1.830

0 (Isotropic)

Anomalously Biaxial

 

 

Garnet: Andradite

1.887

0 (Isotropic)

Isotropic

 

 

Garnet: Demantoid

1.880 - 1.890

0 (Isotropic)

Isotropic

 

 

Garnet: Grossular

1.731 - 1.754

0 (Isotropic)

Isotropic

 

 

Garnet: Hessonite

1.742 - 1.748

0 (Isotropic)

Isotropic

 

 

Garnet: Hydrogrossular

1.680 - 1.712

0 (Isotropic)

Isotropic

 

 

Garnet: Melanite

1.855 - 1.895

0 (Isotropic)

Isotropic

 

 

Garnet: Pyrope

1.720 - 1.756

0 (Isotropic)

Isotropic

 

 

Garnet: Rhodolite

1.760 +/-

0 (Isotropic)

Isotropic

 

 

Garnet: Rosolite

1.731 - 1.754

0 (Isotropic)

Isotropic

 

 

Garnet: Spessartine

1.789 - 1.820

0 (Isotropic)

Isotropic

 

 

Garnet: Topazolite

1.855 - 1.895

0 (Isotropic)

Isotropic

 

 

Garnet: Tsavorite

1.735 - 1.744

0 (Isotropic)

Isotropic

 

 

Garnet: Umbalite

1.735 - 1.744

0 (Isotropic)

Isotropic

 

 

Garnet: Uvarovite

1.865

0 (Isotropic)

Isotropic

 

 

Gaspeite

1.610 - 1.830

0.220

Uniaxial (-)

 

 

Gaudefroyite

1.805 - 2.020

0.210

Uniaxial (+)

 

 

Gaylussite

1.444 - 1.523

0.079

Biaxial (-)

 

 

Genthelvite

1.738 - 1.752

0 (Isotropic)

Isotropic

 

 

Gilalite

1.560 - 1.635

0.075

Biaxial (-)

 

 

Glauberite

1.507 - 1.536

0.022

Biaxial (-)

 

 

Gmelinite-Na

1.476 - 1.494

0.002 - 0.014

Uniaxial (+/-)

 

 

Golden Beryl (Heliodor)

1.566 - 1.579

0.005 - 0.009

Uniaxial (-)

 

 

Goosecreekite

1.495 - 1.502

0.007

Biaxial (-)

 

 

Görgeyite

1.560 - 1.584

0.024

Biaxial (+)

 

 

Gormanite

1.619 - 1.660

0.041

Biaxial (-)

 

 

Goshenite (Beryl)

1.562 - 1.615

0.003 - 0.010

Uniaxial (-)

 

 

Graftonite

1.695 - 1.736

0.024 - 0.027

Biaxial (+)

 

 

Grandidierite

1.590 - 1.639

0.033 - 0.037

Biaxial (-)

 

 

Greenlandite (Fuchsite)

1.552 - 1.618

0.035 - 0.042

Biaxial (-)

 

 

Grossular (Garnet)

1.731 - 1.754

0 (Isotropic)

Isotropic

 

 

Gypsum

1.519 - 1.530

0.010

Biaxial (+)

 

 

Gyrolite

1.535 - 1.549

0.014

Biaxial (-)

 

 

 

 

 

 

 

H
 

RI values

Birefringence

Optics

 

 

Hackmanite

1.483 - 1.487

0 (Isotropic)

Isotropic

 

 

Halite

1.5443

0 (Isotropic)

Isotropic

 

 

Hambergite

1.554 - 1.631

0.074

Biaxial (+)

 

 

Hanksite

1.461 - 1.481

0.020

Uniaxial (-)

 

 

Hardystonite

1.661 - 1.672

0.011

Uniaxial (-)

 

 

Hauerite

2.690

0 (Isotropic)

Isotropic

 

 

Haüyne

1.494 - 1.509

0 (Isotropic)

Isotropic

 

 

Hedenbergite

1.669 - 1.757

0.029

Biaxial (+)

 

 

Heliodor (Beryl)

1.566 - 1.579

0.005 - 0.009

Uniaxial (-)

 

 

Helvine

1.728 - 1.749

0 (Isotropic)

Isotropic

 

 

Helvite (Helvine)

1.728 - 1.749

0 (Isotropic)

Isotropic

 

 

Hematite

2.870 - 3.220

0.280

Uniaxial (-)

 

 

Hemimorphite

1.614 - 1.636

0.022

Biaxial (+)

 

 

Henmilite

1.585 - 1.615

0.030

Biaxial (-)

 

 

Herderite

1.556 - 1.620

0.033

Biaxial (-)

 

 

Hessonite (Garnet)

1.742 - 1.748

0 (Isotropic)

Isotropic

 

 

Heulandite

1.491 - 1.512

0.009

Biaxial (+)

 

 

Hexagonite (Tremolite)

1.599 - 1.637

0.023 - 0.028

Biaxial (-)

 

 

Hibonite

1.790 - 1.807

0.017

Uniaxial (-)

 

 

Hiddenite (Spodumene)

1.657 - 1.681

0.014 - 0.016

Biaxial (+)

 

 

Hodgkinsonite

1.720 - 1.746

0.026

Biaxial (-)

 

 

Hopeite

1.572 - 1.592

0.018

Biaxial (-)

 

 

Howlite

1.583 - 1.600

0.017

Biaxial (-)

 

 

Hübnerite 

2.170 - 2.320

0.130

Biaxial (+)

 

 

Humite

1.607 - 1.675

0.032

Biaxial (+)

 

 

Hureaulite

1.637 - 1.671

0.012 - 0.015

Biaxial (-)

 

 

Hyalite (Opal)

1.440 - 1.460

0 (Isotropic)

Isotropic

 

 

Hyalophane (Microcline)

1.542 - 1.547

0.005

Biaxial (-)

 

 

Hydroboracite

1.520 - 1.571

0.049

Biaxial (+)

 

 

Hydrogrossular (Garnet)

1.680 - 1.712

0 (Isotropic)

Isotropic

 

 

Hydrohetaerolite

2.102 - 2.262

0.160

Uniaxial (-)

 

 

Hydroxylherderite

1.589 - 1.643

0.029 - 0.030

Biaxial (-)

 

 

Hydrozincite

1.630 - 1.750

0.120

Biaxial (-)

 

 

Hypersthene

1.669 - 1.773

0.011 - 0.018

Biaxial (-)

 

 

 

 

 

 

 

I
 

RI values

Birefringence

Optics

 

 

Idocrase (Vesuvianite)

1.703 - 1.752

0.003 - 0.006

Uniaxial (+/-)

 

 

Ilvaite

1.727 - 1.883

0.156

Biaxial (+)

 

 

Inderborite

1.482 - 1.530

0.048

Biaxial (-)

 

 

Inderite

1.488 - 1.505

0.017

Biaxial (+)

 

 

Indicolite (Tourmaline)

1.614 - 1.666

0.014 - 0.040

Uniaxial (-)

 

 

Inyoite

1.495 - 1.520

0.025

Biaxial (-)

 

 

Iolite (Cordierite)

1.527 - 1.578

0.011 - 0.018

Biaxial (-)

 

 

 

 

 

 

 

J
 

RI values

Birefringence

Optics

 

 

Jadeite

1.488 - 1.505

0.017

Biaxial (+)

 

 

Jamesonite

1.635 - 1.663

0.022

Biaxial (-)

 

 

Jeremejevite

1.640 - 1.653

0.013

Uniaxial (-)

 

 

Jet

1.440 - 1.460

0 (Isotropic)

Isotropic

 

 

Johachidolite

1.712 - 1.726

0.014

Biaxial (+)

 

 

Johannsenite

1.703 - 1.745

0.029

Biaxial (+)

 

 

Johnsenite-(Ce)

1.637 - 1.648

0.011

Uniaxial (-)

 

 

 

 

 

 

 

K
 

RI values

Birefringence

Optics

 

 

Kaersutite

1.670 - 1.772

0.030 - 0.083

Biaxial (-)

 

 

Kaliborite

1.508 - 1.550

0.042

Biaxial (+)

 

 

Kämmererite

1.571 - 1.597

0.003

Biaxial (+/-)

 

 

Kaolinite

1.553 - 1.570

0.007 - 0.017

Biaxial (-)

 

 

Katophorite

1.640 - 1.692

0.020

Biaxial (-)

 

 

Kentbrooksite

1.623 - 1.628

0.005

Uniaxial (-)

 

 

Kernite

1.454 - 1.488

0.034

Biaxial (-)

 

 

Kinoite

1.638 - 1.676

0.038

Biaxial (-)

 

 

Kolwezite

1.688 - 1.900

0.212

Biaxial (-)

 

 

Korite

1.520 - 1.670

0.150

 

 

 

Kornerupine

1.660 - 1.684

0.014

Biaxial (-)

 

 

Kovdorskite

1.527 - 1.549

0.022

Biaxial (-)

 

 

Kröhnite

1.544 - 1.601

0.057

Biaxial (-)

 

 

Kulanite

1.703 - 1.723

0.020

Biaxial (+)

 

 

Kunzite (Spodumene)

1.657 - 1.681

0.014 - 0.016

Biaxial (+)

 

 

Kurchatovite

1.635 - 1.698

0.063

Biaxial (-)

 

 

Kurnakovite

1.488 - 1.525

0.027 - 0.034

Biaxial (-)

 

 

Kutnohorite

1.519 - 1.727

0.191 - 0.0192

Uniaxial (-)

 

 

Kyanite 

1.712 - 1.734

0.015 - 0.016

Biaxial (-)

 

 

 

 

 

 

 

L
 

RI values

Birefringence

Optics

 

 

Labradorite

1.554 - 1.573

0.008 - 0.010

Biaxial (+)

 

 

Lapis Lazuli

1.500 - 1.670

0 (Isotropic)

Isotropic

 

 

Larimar (Pectolite)

1.594 - 1.642

0.037

Biaxial (+)

 

 

Laumontite

1.502 - 1.525

0.012

Biaxial (-)

 

 

Lawsonite

1.665 - 1.686

0.019 - 0.021

Biaxial (+)

 

 

Lazulite

1.604 - 1.663

0.033 - 0.037

Biaxial (-)

 

 

Lazurite

1.502 - 1.522

0 (Isotropic)

Isotropic

 

 

Leadhillite

1.870 - 2.010

0.140

Biaxial (-)

 

 

Legrandite

1.675 - 1.740

0.060 - 0.066

Biaxial (+)

 

 

Leifite

1.511 - 1.522

0.011

Uniaxial (+)

 

 

Lepidocrocite

1.940 - 2.510

0.570

Biaxial (-)

 

 

Lepidolite

1.525 - 1.587

0.018 - 0.038

Biaxial (-)

 

 

Leucite 

1.508 - 1.509

0.001

Uniaxial (+)

 

 

Leucophanite

1.571 - 1.598

0.027

Biaxial (-)

 

 

Leucophoenicite

1.751 - 1.782

0.031

Biaxial (-)

 

 

Libyan Desert Glass

1.460 - 1.465

-

-

 

 

Liddicoatite 

1.621 - 1.637

0.016

Uniaxial (-)

 

 

Linarite

1.809 - 1.859

0.050

Biaxial (-)

 

 

Lithiopilite

1.663 - 1.691

0.008 - 0.010

Biaxial (+)

 

 

Lizardite 

1.541 - 1.568

0.012

Biaxial (-)

 

 

Londonite

1.6935 - 1.694

0 (Isotropic)

Isotropic

 

 

Lorenzenite

1.910 - 2.060

0.120

Biaxial (-)

 

 

Ludlamite 

1.650 - 1.697

0.038 - 0.044

Biaxial (+)

 

 

Ludwigite

1.830 - 2.020

0.110 - 0.170

Biaxial (+)

 

 

 

 

 

 

 

M
 

RI values

Birefringence

Optics

 

 

MacFallite

1.773 - 1.815

0.037 - 0.040

Biaxial (-)

 

 

Magnesio-Axinite

1.672 - 1.704

0.009 - 0.011

Biaxial (-)

 

 

Magnesio-Riebeckite

1.668 - 1.680

0.012

Biaxial (-)

 

 

Magnesiotaaffeite-2N'2S

1.722 - 1.777

0.055

Uniaxial (+)

 

 

Magnesiotaaffeite-6N'3S

1.735 - 1.739

0.004

Uniaxial (-)

 

 

Magnesite

1.509 - 1.700

0.191

Uniaxial (-)

 

 

Magnetite

2.420

0 (Isotropic)

Isotropic

 

 

Malachite

1.655 - 1.909

0.254

Biaxial (-)

 

 

Mandarin Garnet (Spessartine)

1.789 - 1.820

0 (Isotropic)

Isotropic

 

 

Manganite

2.250 - 2.530

0.028

Biaxial (+)

 

 

Manganoan Adamite

1.708 - 1.773

0.055

Biaxial (+/-)

 

 

Manganotantalite

2.140 - 2.340

0.200

Biaxial (+)

 

 

Mansfieldite

1.622 - 1.663

0.020 - 0.032

Biaxial (+)

 

 

Marialite

1.532 - 1.550

0.007 - 0.009

Uniaxial (-)

 

 

Maw-sit-sit

1.760 - 1.781

0.015

Biaxial

 

 

Meionite

1.556 - 1.600

0.034 - 0.038

Uniaxial (-)

 

 

Melanite

1.855 - 1.895

0 (Isotropic)

Isotropic

 

 

Melanterite

1.470 - 1.486

0.016

Biaxial (+)

 

 

Meliphanite

1.592 - 1.672

0.019

Uniaxial (-)

 

 

Mellite

1.511 - 1.539

0.028

Uniaxial (-)

 

 

Meta-Autunite

1.584 - 1.630

0.015 - 0.023

Uniaxial (-)

 

 

Meyerhofferite

1.500 - 1.560

0.060

Biaxial (-)

 

 

Microcline

1.514 - 1.539

0.007 - 0.010

Biaxial (-)

 

 

Microlite

1.993 - 2.020

0 (Isotropic)

Isotropic

 

 

Milarite

1.529 - 1.551

0.003

Uniaxial (-)

 

 

Mimetite

2.128 - 2.147

0.019

Uniaxial (-)

 

 

Moldavite

1.480 - 1.540

0 (Isotropic)

Isotropic

 

 

Monazite

1.770 - 1.860

0.053 - 0.067

Biaxial (+)

 

 

Montebrasite

1.594 - 1.645

0.022 - 0.030

Biaxial (+/-)

 
 

Montgomeryite

1.572 - 1.582

0.010

Biaxial (-)

 
 

Montmorillonite

1.485 - 1.550

0.020

Biaxial (-)

 
 

Moonstone (Feldspar)

1.518 - 1.527

0.006 - 0.007

Biaxial (-)

 
 

Mordenite

1.472 - 1.487

0.005

Biaxial (+/-)

 
 

Morganite (Beryl)

1.573 - 1.600

0.005 - 0.009

Uniaxial (-)

 
 

Morion (Quartz)

1.544 - 1.553

0.009

Uniaxial (+)

 
 

Mosandrite 

1.646 - 1.658

0.012

Biaxial (+)

 
 

Mottramite

2.170(2) - 2.320(2)

0.150

Biaxial (-)

 
 

Mtorodite (Chalcedony)

1.530 - 1.543

0.003 - 0.009

Uniaxial (+)

 
 

Mtorolite (Chalcedony)

1.530 - 1.543

0.003 - 0.009

Uniaxial (+)

 
 

Muscovite

1.552 - 1.618

0.035 - 0.042

Biaxial (-)

 
 

Musgravite 

1.735 - 1.739

0.004

Uniaxial (-)

 

 

Myrickite (Chalcedony)

1.530 - 1.543

0.003 - 0.009

Uniaxial (+)

 

 

 

 

 

 

 

N
 

RI values

Birefringence

Optics

 

 

Nambulite 

1.707 - 1.730

0.023

Biaxial (+)

 

 

Narsarsukite

1.609 - 1.630

0.021

Uniaxial (+)

 

 

Natrolite

1.473 - 1.496

0.012 - 0.013

Biaxial (+)

 
 

Natrosilite

1.507 - 1.521

0.014

Biaxial (-)

 
 

Neotocite

1.500 - 1.650

0 (Isotropic)

Isotropic

 
 

Nepheline

1.529 - 1.542

0.003 - 0.004

Uniaxial (-)

 
 

Neptunite

1.690 - 1.736

0.029 - 0.045

Biaxial (+)

 
 

Nifontovite

1.575 - 1.584

0.009

Biaxial (+)

 
 

Norbergite

1.563 - 1.593

0.027

Biaxial (+)

 
 

Nuummite

1.635 - 1.663

0.022

Biaxial (-)

 
         

 

O
 

RI values

Birefringence

Optics

 
 

Obsidian 

1.450 - 1.550

0 (Isotropic)

Isotropic

 
 

Oligoclase (Feldspar)

1.538 - 1.550

0.010

Biaxial (-)

 
 

Olivine (Peridot)

1.650 - 1.710

0.035 - 0.038

Biaxial (+)

 
 

Olmiite

1.663(1) - 1.694(1)

0.031

Biaxial (+)

 
 

Opal

1.400 - 1.460

0 (Isotropic)

Isotropic

 
 

Orpiment

2.400 - 3.020

0.620

Biaxial (-)

 
 

Orthoclase (Feldspar)

1.518 - 1.525

0.004 - 0.005

Biaxial (-)

 
         

 

P
 

RI values

Birefringence

Optics

 
 

Painite

1.788 - 1.816

0.028

Uniaxial (-)

 
 

Pargasite

1.630 - 1.650

0.020

Biaxial (-)

 
 

Parisite

1.676 - 1.757

0.081

Uniaxial (+)

 
 

Pectolite

1.594 - 1.642

0.037

Biaxial (+)

 
 

Pentagonite

1.533 - 1.547

0.014

Biaxial (-)

 
 

Periclase

1.732

0 (Isotropic)

Isotropic

 
 

Peridot (Olivine)

1.650 - 1.710

0.035 - 0.038

Biaxial (+)

 
 

Perovskite

2.300 - 2.380

0.080

Biaxial (+)

 
 

Petalite

1.504 - 1.516

0.012

Biaxial (+)

 
 

Petedunnite

1.680 - 1.700

0.020

Biaxial (+)

 
 

Petschite (Scapolite)

1.540 - 1.579

0.006 - 0.037

Uniaxial (-)

 
 

Pezzottaite

1.601 - 1.620

0.011

Uniaxial (-)

 
 

Phenakite (Phenacite)

1.650 - 1.670

0.017

Uniaxial (+)

 
 

Phlogopite

1.530 - 1.618

0.028 - 0.045

Biaxial (-)

 
 

Phosgenite

2.118 - 2.145

0.027

Uniaxial (+)

 
 

Phosphophyllite

1.595 - 1.620

0.021

Biaxial (-)

 
 

Phosphosiderite

1.692 - 1.738

0.046

Biaxial (-)

 
 

Piemontite

1.725 - 1.832

0.025 - 0.076

Biaxial (+)

 
 

Pirssonite

1.504 - 1.575

0.071

Biaxial (+)

 
 

Plancheite

1.645 - 1.715

0.070

Biaxial (+)

 
 

Pleonaste

1.780

0 (Isotropic)

Isotropic

 
 

Poldervaartite

1.634 - 1.656

0.022

Biaxial (+)

 
 

Pollucite

1.508 - 1.528

0 (Isotropic)

Isotropic

 
 

Polylithionite

1.530 - 1.559

0.025 - 0.029

Biaxial (-)

 
 

Potassic-fluoro-hastingsite

1.668 - 1.698

0.030

Biaxial (-)

 
 

Poudretteite

1.511 - 1.532

0.021

Uniaxial (+)

 
 

Povondraite

1.751 - 1.820

0.069

Uniaxial (-)

 
 

Powellite

1.974 - 1.984

0.010

Uniaxial (+)

 
 

Prase (Quartz)

1.544 - 1.553

0.009

Uniaxial (+)

 
 

Prasiolite (Quartz)

1.544 - 1.553

0.009

Uniaxial (+)

 
 

Prehnite

1.611 - 1.665

0.021 - 0.033

Biaxial (+)

 
 

Priceite

1.571 - 1.594

0.022

Biaxial (-)

 
 

Prismatine

1.669 - 1.830

0.013

Biaxial (-)

 
 

Prosopite

1.501 - 1.510

0.009

Biaxial (+)

 
 

Proustite

2.792 - 3.088

0.295 - 0.296

Uniaxial (-)

 
 

Pumpellyite

1.674 - 1.764

0.014 - 0.016

Biaxial (+)

 
 

Purpurite

1.852(2) - 1.922(2)

0.040 - 0.070

Biaxial (+)

 
 

Pyrargyrite

2.881 - 3.084

0.203

Uniaxial (-)

 
 

Pyromorphite

2.048 - 2.058

0.010

Uniaxial (-)

 
 

Pyrope (Garnet)

1.720 - 1.756

0 (Isotropic)

Isotropic

 
 

Pyrophyllite

1.534 - 1.601

0.062

Biaxial (-)

 
 

Pyroxmangite

1.726 - 1.764

0.018

Biaxial (+)

 
         

 

Q
 

RI values

Birefringence

Optics

 
 

Quartz

1.544 - 1.553

0.009

Uniaxial (+)

 
         

 

R
 

RI values

Birefringence

Optics

 
 

Realgar

2.538 - 2.704

0.166

Biaxial (-)

 
 

Red Beryl (Bixbite)

1.568 - 1.595

0.004 - 0.007

Uniaxial (-)

 
 

Reidite (Zircon)

1.925 - 2.015

0.055

Uniaxial (+)

 
 

Rémondite

1.632 - 1.638

0.006

Biaxial (+)

 
 

Rhodizite

1.684 - 1.694

0 (Isotropic)

Isotropic

 
 

Rhodochrosite 

1.596 - 1.816

0.218

Uniaxial (-)

 
 

Rhodolite (Garnet)

1.760 (+/-)

0 (Isotropic)

Isotropic

 
 

Rhodonite

1.711 - 1.751

0.013

Biaxial (+)

 
 

Richterite

1.615 - 1.636

0.021

Biaxial (-)

 
 

Rockbridgeite

1.873 - 1.897

0.022

Biaxial (+)

 
 

Roeblingite

1.640 - 1.660

0.020

Biaxial (+)

 
 

Rosasite

1.672 - 1.831

0.139 - 0.143

Biaxial (-)

 
 

Roselite 

1.694 - 1.735

0.018 - 0.025

Biaxial (-)

 
 

Rose Quartz

1.544 - 1.553

0.009

Uniaxial (+)

 
 

Rosolite (Grossular)

1.731 - 1.754

0 (Isotropic)

Isotropic

 
 

Rossmanite

1.624 - 1.645

0.021

Uniaxial (-)

 
 

Rubellite (Tourmaline)

1.614 - 1.666

0.014 - 0.040

Uniaxial (-)

 
 

Ruby

1.762 - 1.778

0.008

Uniaxial (-)

 
 

Rutile

2.605 - 2.901

0.294

Uniaxial (+)

 
         

 

S
 

RI values

Birefringence

Optics

 
 

Sadanagaite

1.673 - 1.697

0.024

Biaxial (-)

 
 

Salammoniac

1.693

0 (Isotropic)

Isotropic

 
 

Samarskite-(Y)

2.100 -2.200

0 (Isotropic)

Isotropic

 
 

Sanidine

1.518 - 1.531

0.007

Biaxial (-)

 
 

Sapphire

1.762 - 1.788

0.008 - 0.009

Uniaxial (-)

 
 

Sapphirine

1.701 - 1.734

0.004 -0.005

Biaxial (-)

 
 

Sarcopside

1.670 - 1.734

0.060

Biaxial (-)

 
 

Scapolite

1.540 - 1.579

0.006 - 0.037

Uniaxial (-)

 
 

Scheelite

1.918 - 1.938

0.017

Uniaxial (+)

 
 

Scheuchzerite

1.740 - 1.750

0.010

Biaxial (+)

 
 

Schlossmacherite

1.597

0.000

Uniaxial (+)

 
 

Schorl

1.635 - 1.672

0.025

Uniaxial (-)

 
 

Scolecite

1.507 - 1.521

0.010

Biaxial (-)

 
 

Scorodite

1.741 - 1.820

0.027 - 0.036

Biaxial (+)

 
 

Scorzalite

1.626 - 1.680

0.036 - 0.037

Biaxial (-)

 
 

Searlesite

1.516 - 1.535

0.019

Biaxial (-)

 
 

Selenite

1.519 - 1.530

0.010

Biaxial (+)

 
 

Sellaite

1.378 - 1.390

0.012

Uniaxial (+)

 
 

Sénarmontite

2.087

0 (Isotropic)

Isotropic

 
 

Sérandite

1.668 - 1.703

0.035

Biaxial (+)

 
 

Seraphinite (Clinochlore)

1.571 - 1.599

0.005 - 0.011

Biaxial (+)

 
 

Serendibite

1.701 - 1.706

0.005

Biaxial (+)

 
 

Serpentine (Antigorite)

1.555 - 1.573

0.005 - 0.006

Biaxial (-)

 
 

Serpentine (Chrysotile)

1.569 - 1.570

0.001

Biaxial

 
 

Serpentine (Lizardite)

1.541 - 1.568

0.012

Biaxial (-)

 
 

Shattuckite

1.753 - 1.815

0.062

Biaxial (+)

 
 

Shomiokite

1.528 - 1.531

0.003

Biaxial (+)

 
 

Shortite

1.531 - 1.570

0.039

Biaxial (-)

 
 

Siderite

1.633 - 1.875

0.242

Uniaxial (-)

 
 

Sillimanite

1.653 - 1.684

0.016 - 0.023

Biaxial (+)

 
 

Simpsonite

2.025 - 2.045

0.020

Uniaxial (-)

 
 

Sinhalite

1.665 - 1.712

0.036 - 0.042

Biaxial (-)

 
 

Sklodowskite

1.654 - 1.667

0.010 - 0.012

Biaxial (-)

 
 

Smithsonite 

1.619 - 1.850

0.223 - 0.227

Uniaxial (+)

 
 

Smoky Quartz

1.544 - 1.553

0.009

Uniaxial (+)

 
 

Sodalite

1.483 - 1.487

0 (Isotropic)

Isotropic

 
 

Soddyite

1.650 - 1.715

0.049 - 0.061

Biaxial (-)

 
 

Sogdianite 

1.606 - 1.608

0.002

Uniaxial (+)

 
 

Spessartine (Garnet)

1.789 - 1.820

0 (Isotropic)

Isotropic

 
 

Sphalerite 

2.369

0 (Isotropic)

Isotropic

 
 

Sphene (Titanite)

1.843 - 2.110

0.100 - 0.160

Biaxial (+)

 
 

Spherocobaltite 

1.600 - 1.855

0.255

Uniaxial (-)

 
 

Spinel

1.719

0 (Isotropic)

Isotropic

 
 

Spodumene

1.648 - 1.679

0.014 - 0.018

Biaxial (+)

 
 

Spurrite

1.640 - 1.681

0.039 - 0.040

Biaxial (-)

 
 

Srilankite

2.380

0.000

Biaxial (-)

 
 

Staurolite

1.736 - 1.762

0.009 - 0.015

Biaxial (+)

 
 

Steacyite

1.572 - 1.573

0.001

Uniaxial (-)

 
 

Stellerite

1.485 - 1.498

0.013

Biaxial (-)

 
 

Stibiotantalite 

2.374 - 2.457

0.083

Biaxial (+)

 
 

Stichtite

1.516 - 1.542

0.026

Uniaxial (+)

 
 

Stilbite

1.484 - 1.513

0.010 - 0.013

Biaxial (-)

 
 

Stolzite

2.180 - 2.270

0.090

Uniaxial (-)

 
 

Sturmanite

1.497 - 1.505

0.002

Uniaxial (+/-)

 
 

Sugilite

1.607 - 1.610

0.003

Uniaxial (-)

 
 

Sulphohalite

-

0 (Isotropic)

Isotropic

 
 

Sulfur (Sulphur)

1.958 - 2.245

0.287

Biaxial (+)

 
 

Sunstone (Feldspar)

1.525 - 1.552

0.007 - 0.010

Biaxial (-)

 
 

Suolunite

1.610 - 1.623

0.013

Biaxial (-)

 
 

Sursassite

1.736 - 1.766

0.030

Biaxial (-)

 
 

Sussexite

1.670 - 1.732

0.062

Biaxial (-)

 
 

Svabite 

1.698 - 1.706

0.008

Uniaxial (-)

 
 

Synchysite-(Y)

1.653 - 1.730

0.077

Biaxial

 
 

Syngenite

1.501 - 1.518

0.017

Biaxial (-)

 
 

Szaibelyite 

1.530 - 1.740

0.020 - 0.070

Biaxial (-)

 
         

 

T
 

RI values

Birefringence

Optics

 
 

Taaffeite

1.722 - 1.777

0.055

Uniaxial (+)

 
 

Takovite

1.600 - 1.602

0.001 - 0.002

Uniaxial (-)

 
 

Talc

1.538 - 1.600

0.051

Biaxial (-)

 
 

Tantalite-(Fe)

2.260 - 2.430

0.170

Biaxial (-)

 
 

Tantalite-(Mn)

2.140 - 2.340

0.200

Biaxial (+)

 
 

Tanzanite

1.685 - 1.707

0.006 - 0.013

Biaxial (+)

 
 

Taranakite

1.500 - 1.510

0.006 - 0.007

Uniaxial (-)

 
 

Tarbuttite

1.660 - 1.713

0.053

Biaxial (-)

 
 

Tashmarine (Diopside)

1.663 - 1.728

0.030

Biaxial (+)

 
 

Tephroite

1.759 - 1.860

0.101

Biaxial (-)

 
 

Thaumasite

1.468 - 1.507

0.039

Uniaxial (-)

 
 

Thénardite

1.471 - 1.484

0.013

Biaxial (+)

 
 

Thomsonite

1.511 - 1.545

0.005 - 0.015

Biaxial (+)

 
 

Thorite

1.780 - 1.840

0.010 - 0.020

Uniaxial (-)

 
 

Thulite

1.695(+/-)

0.006 - 0.013

Biaxial (+)

 
 

Tilasite

1.640 - 1.675

0.035

Biaxial (-)

 
 

Tilleyite

1.612 - 1.654

0.040

Biaxial (+)

 
 

Tinaksite

1.593 - 1.666

0.073

Biaxial (+)

 
 

Tincalconite

1.461 - 1.474

0.013

Uniaxial (+)

 
 

Tinzenite

1.693 - 1.704

0.011

Biaxial (-)

 
 

Titanite (Sphene)

1.843 - 2.110

0.100 - 0.160

Biaxial (+)

 
 

Topaz

1.606 - 1.638

0.010

Biaxial (+)

 
 

Topazolite

1.855 - 1.895

0 (Isotropic)

Isotropic

 
 

Tourmaline: Achroite

1.614 - 1.666

0.014 - 0.040

Uniaxial (-)

 
 

Tourmaline: Dravite

1.612 - 1.661

0.022 - 0.029

Uniaxial (-)

 
 

Tourmaline: Elbaite

1.615 - 1.651

0.018 - 0.021

Uniaxial (-)

 
 

Tourmaline: Indicolite

1.614 - 1.666

0.014 - 0.040

Uniaxial (-)

 
 

Tourmaline: Liddicoatite 

1.621 - 1.637

0.016

Uniaxial (-)

 
 

Tourmaline: Povondraite

1.751 - 1.820

0.069

Uniaxial (-)

 
 

Tourmaline: Rossmanite

1.624 - 1.645

0.021

Uniaxial (-)

 
 

Tourmaline: Rubellite

1.614 - 1.666

0.014 - 0.040

Uniaxial (-)

 
 

Tourmaline: Schorl

1.635 - 1.672

0.025

Uniaxial (-)

 
 

Tourmaline: Uvite

1.619 - 1.668

0.018 - 0.029

Uniaxial (-)

 
 

Tourmaline: Verdelite

1.614 - 1.666

0.014 - 0.040

Uniaxial (-)

 
 

Tremolite

1.599 - 1.637

0.026

Biaxial (-)

 
 

Tremolite, Chrome

1.599 - 1.637

0.023 - 0.028

Biaxial (-)

 
 

Triphylite

1.685 - 1.720

0.004

Biaxial (+/-)

 
 

Triplite

1.650 - 1.680

0.030

Biaxial (+)

 
 

Trolleite

1.619 - 1.643

0.024

Biaxial (-)

 
 

Trona

1.412 - 1.540

0.128

Biaxial (-)

 
 

Tsavorite (Garnet)

1.735 - 1.744

0 (Isotropic)

Isotropic

 
 

Tschermakite

1.623 - 1.688

0.015 - 0.028

Biaxial (-)

 
 

Tsilaisite

1.625(5) - 1.645(5)

0.020

Uniaxial (-)

 
 

Tugtupite

1.496 - 1.502

0.006

Uniaxial (+)

 
 

Turquoise

1.610 - 1.650

0.040

Biaxial (+)

 
         

 

U
 

RI values

Birefringence

Optics

 
 

Ulexite

1.491 - 1.520

0.028

Biaxial (+)

 
 

Ussingite

1.504 - 1.545

0.041

Biaxial (+)

 
 

Uvarovite (Garnet)

1.865

0 (Isotropic)

Isotropic

 
 

Uvite (Tourmaline)

1.619 - 1.668

0.018 - 0.029

Uniaxial (-)

 
         

 

V
 

RI values

Birefringence

Optics

 
 

Vanadinite

2.235 - 2.416

0.066

Uniaxial (-)

 
 

Vandenbrandeite

1.765 - 1.800

0.035

Biaxial (-)

 
 

Variscite

1.563 - 1.594

0.031

Biaxial (-)

 
 

Väyrynenite

1.638 - 1.667

0.026 - 0.027

Biaxial (-)

 
 

Verdite

1.580 (+/-)

-

Biaxial (-)

 
 

Vesuvianite

1.700 - 1.752

0.003 - 0.006

Uniaxial (+/-)

 
 

Veszelyite

1.618 - 1.695

0.040 - 0.055

Biaxial (+)

 
 

Villiaumite

1.328 - 1.332

0 (Isotropic)

Isotropic

 
 

Violane

1.668 - 1.703

0.024 - 0.030

Biaxial (+)

 
 

Viridine

1.629 - 1.660

0.007 - 0.013

Biaxial (-)

 
 

Vivianite

1.579 - 1.675

0.050 - 0.059

Biaxial (+)

 
 

Vlasovite

1.607 - 1.628

0.021

Biaxial (-)

 
 

Volkonskoite

1.551 - 1.569

0.018

Biaxial (-)

 
         

 

W
 

RI values

Birefringence

Optics

 
 

Wardite

1.586 - 1.604

0.009

Uniaxial (+)

 
 

Wavellite

1.518 - 1.561

0.026

Biaxial (+)

 
 

Weloganite 

1.558 - 1.646

0.082

Biaxial (-)

 
 

Wendwilsonite

1.694 - 1.713

0.019

Biaxial (+)

 
 

Wernerite (Scapolite)

1.540 - 1.579

0.006 - 0.037

Uniaxial (-)

 
 

Whewellite

1.489 - 1.650

0.160

Biaxial (+)

 
 

Willemite 

1.691 - 1.725

0.028

Uniaxial (+)

 
 

Williamsite

1.530 - 1.575

-

Biaxial (-)

 
 

Wiluite

1.721 - 1.725

0.004

Uniaxial (+)

 
 

Witherite

1.529 - 1.677

0.148

Biaxial (-)

 
 

Wollastonite

1.616 - 1.653

0.015

Biaxial (-)

 
 

Woodhouseite

1.636 - 1.647

0.011

Uniaxial (+)

 
 

Wulfenite 

2.283 - 2.405

0.122

Uniaxial (-)

 
 

Wurtzite

2.356 - 2.378

0.022

Uniaxial (+)

 
         

 

X
 

RI values

Birefringence

Optics

 
 

Xenotime

1.720 - 1.827

0.096

Uniaxial (+)

 
 

Xonotlite

1.583 - 1.595

0.012

Biaxial (+)

 
         

 

Y
 

RI values

Birefringence

Optics

 
 

Yttrocrasite-(Y)

2.120 - 2.150

0 (Isotropic)

Isotropic

 
 

Yugawaralite

1.495 - 1.504

0.009

Biaxial (+)

 
 

Yuksporite

1.644 - 1.660

0.016

Biaxial (+)

 
         

 

Z
 

RI values

Birefringence

Optics

 
 

Zektzerite 

1.582 - 1.584

0.002

Biaxial (-)

 
 

Zincite 

2.013 - 2.048

0.016

Uniaxial (+)

 
 

Zircon

1.925 - 2.015

0.055

Uniaxial (+)

 
 

Zoisite 

1.696 - 1.718

0.006 - 0.018

Biaxial (+)

 
 

Zunyite

1.600 - 1.650

0 (Isotropic)

Isotropic

 
 

Zwieselite

1.686 - 1.713

0.017

Biaxial (+)

 
           

 

Notes:
Values may be approximate or may vary by mineral origin and associations with other minerals, inclusions, and by cleanliness and quality of gemstone polish.

References:
• Color Encyclopedia of Gemstones, Second Edition (1987), by Joel E. Arem.
gemdat.org

mindat.org

 


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