ClassicGems.net

Birefringence

Birefringence is the difference between the high and low Refractive Index (RI) values of a gemstone. Careful rotation of the gemstone and repeated readings on a refractometer will usually provide the maximum spread between the refractive indices which is equal to the Birefringence of the gemstone. Birefringence values are often useful in quickly narrowing possible choices during gemstone indentification work. The first list below is in alphabetical order. The second list is in numerical order of birefrigence from highest to lowest.

Birefringence of Gems

Birefringence

RI values

Optics

Achroite (Tourmaline)

0.014 - 0.040

1.614 - 1.666

Uniaxial (-)

Acmite (Aegirine)

0.037 - 0.061

1.720 - 1.839

Biaxial (-)

Actinolite

0.023

1.613 - 1.666

Biaxial (-)

Adamite

0.055

1.708 - 1.773

Biaxial (+/-)

Adularia (Microcline)

0.007 - 0.010

1.514 - 1.539

Biaxial (-)

Adventurine (Quartz)

0.009

1.543 - 1.554

Uniaxial (+)

Aegirine

0.037-0.061

1.720 - 1.839

Biaxial (-)

Aenigmatite

0.090 - 0.100

1.780 - 1.900

Biaxial (+)

Aerinite

0.070

1.510 - 1.580

Biaxial (-)

Aeschynite-(Y)

0.150 - 0.220

2.190 - 2.500

Biaxial (+)

Afghanite

0.006

1.523 - 1.529

Uniaxial (+)

Agate (Quartz)

0.009

1.543 - 1.554

Uniaxial (+)

Agrellite

0.014

1.567 - 1.581

Biaxial (-)

Ajoite

0.091

1.550 - 1.641

Biaxial (+)

Alabandite

0 (Isotropic)

2.700

Isotropic

Albite (Feldspar)

0.010

1.528 - 1.542

Biaxial (+)

Alexandrite (Chrysoberyl)

0.010

1.746 - 1.756

Biaxial (+)

Allanite-(Ce)

0.018 - 0.031

1.715 - 1.822

Biaxial (-)

Allanite-(La)

0.010

1.755 - 1.765

Biaxial (-)

Almandine (Garnet)

0 (Isotropic)

1.830

Isotropic

Alum-(K)

0 (Isotropic)

1.453

Isotropic

Alunite

0.020

1.572 - 1.592

Uniaxial (+)

Alurgite (Muscovite)

0.035 - 0.042

1.552 - 1.618

Biaxial

Amazonite (Feldspar)

0.007 - 0.010

1.514 - 1.539

Biaxial (-)

Amber

0 (Isotropic)

1.539 - 1.545

Isotropic

Amblygonite

0.019 - 0.022

1.577 - 1.613

Biaxial (-)

Amesite

0.015 - 0.018

1.597 - 1.615

Biaxial (+)

Amethyst (Quartz)

0.009

1.543 - 1.554

Uniaxial (+)

Ametrine (Quartz)

0.009

1.543 - 1.554

Uniaxial (+)

Analcime

0.001

1.479 - 1.494

Biaxial (-)

Anapaite

0.037 - 0.047

1.602 - 1.649

Biaxial (+)

Anatase

0.073

2.488 - 2.561

Uniaxial (-)

Andalusite

0.009 - 0.010

1.629 - 1.650

Biaxial (-)

Andesine (Albite, Feldspar)

0.010

1.528 - 1.542

Biaxial (+)

Andradite (Garnet)

0 (Isotropic)

1.887

Isotropic

Angelite (Anhydrite)

0.042 - 0.044

1.567 - 1.618

Biaxial (+)

Anglesite

0.017

1.878 - 1.895

Biaxial (+)

Anhydrite

0.042 - 0.044

1.567 - 1.618

Biaxial (+)

Annabergite

0.065

1.622 - 1.687

Biaxial (+/-)

Anorthite (Feldspar)

0.012 - 0.013

1.573 - 1.590

Biaxial (-)

Anthophyllite

0.017 - 0.023

1.598 - 1.697

Biaxial (+)

Antigorite

0.005 - 0.006

1.555 - 1.573

Biaxial (-)

Apache Tears (Obsidian)

0 (Isotropic)

1.450 - 1.550

Isotropic

Apatite (Fluorapatite)

0.004

1.631 - 1.646

Uniaxial (-)

Apophyllite

0.002

1.530 - 1.538

Uniaxial (+)

Aquamarine (Beryl)

0.004 - 0.007

1.568 - 1.595

Uniaxial (-)

Aragonite

0.156

1.529 - 1.686

Biaxial (-)

Arfvedsonite

0.014

1.652 - 1.708

Biaxial (-)

Arrojadite-(KFe)

0.011

1.664 - 1.675

Biaxial (+)

Artinite

0.068

1.488 - 1.557

Biaxial (-)

Ascharite (Szaibelyite)

0.020 - 0.070

1.530 - 1.740

Biaxial (-)

Astrophyllite

0.050

1.680 - 1.730

Biaxial (+)

Augelite

0.014 - 0.015

1.574 - 1.588

Biaxial (+)

Augite

0.026 - 0.039

1.680 - 1.774

Biaxial (+)

Aurichalcite

0.089

1.655 - 1.744

Biaxial (-)

Austinite

0.024

1.759(3) - 1.783(3)

Biaxial (+)

Autunite

0.015 - 0.023

1.584 - 1.607

Uniaxial (-)

Axinite-(Fe)

0.009 - 0.011

1.672 - 1.704

Biaxial (-)

Axinite-(Mg)

0.009 - 0.011

1.672 - 1.704

Biaxial (-)

Azurite

0.108

1.730 - 1.838

Biaxial (+)

Birefringence

RI values

Optics

Babingtonite

0.025

1.700 - 1.725

Biaxial (-)

Baddeleyite

0.070

2.130 - 2.200

Biaxial (-)

Bahianite

0.110

1.810 - 1.920

Biaxial (-)

Bakerite

0.030

1.624 - 1.654

Biaxial (-)

Baratovite

0.008

1.666 - 1.674

Biaxial (+)

Barite (Baryte)

0.012

1.636 - 1.648

Biaxial (+)

Barkevikite (Ferro-edenite)

0.020

1.710 - 1.730

Biaxial (-)

Barrerite

0.010

1.479 - 1.489

Biaxial (-)

Bastnäsite-(Ce)

0.101

1.717 - 1.823

Uniaxial (+)

Bementite

0.028 - 0.030

1.602 - 1.650

Biaxial

Benitoite

0.046

1.756 - 1.804

Uniaxial (+)

Bertossaite

0.018

1.624 - 1.642

Biaxial (-)

Bertrandite

0.023

1.591 - 1.614

Biaxial (-)

Beryl Group

0.004 - 0.007

1.568 - 1.602

Uniaxial (-)

Beryllonite

0.009

1.552 - 1.561

Biaxial (-)

Betafite

0 (Isotropic)

1.910 - 2.197

Isotropic

Binghamite (Chalcedony)

0.009

1.543 - 1.554

Uniaxial (+)

Bisbeeite (Chrysocolla)

0.023 - 0.050

1.575 - 1.635

Biaxial (-)

Bixbite (Beryl)

0.004 - 0.007

1.568 - 1.595

Uniaxial (-)

Blödite

0.004

1.483 - 1.487

Biaxial (-)

Bloodstone (Chalcedony)

0.009

1.543 - 1.554

Uniaxial (+)

Boleite

0 (Isotropic)

2.050

Isotropic

Boracite

0.010 - 0.011

1.658 - 1.673

Biaxial (+)

Bowenite (Antigorite)

0.005 - 0.006

1.555 - 1.573

Biaxial (-)

Brazilianite

0.019 - 0.021

1.602 - 1.623

Biaxial (+)

Brochantite

0.072

1.728 - 1.800

Biaxial (-)

Bromellite

0.028

1.705 - 1.733

Uniaxial (+)

Brookite

0.117 - 0.1173

2.583 - 2.700

Biaxial (+)

Bronzite (Enstatite)

0.009 - 0.011

1.650 - 1.679

Biaxial (+)

Brucite

0.020

1.560 - 1.600

Biaxial (+)

Burangaite

0.032

1.611 - 1.643

Biaxial (-)

Burbankite

0.019

1.616 - 1.623

Uniaxial (-)

Burmite (Amber)

0 (Isotropic)

1.539 - 1.545

Isotropic

Buserite

0.040

1.690 - 1.730

Uniaxial (-)

Bustamite

0.013 - 0.015

1.640 - 1.710

Biaxial (-)

Bytownite

0.010 - 0.011

1.563 - 1.583

Biaxial (+/-)

Birefringence

RI values

Optics

Cacoxenite

0.060

1.575 - 1.656

Uniaxial (+)

Calcite

0.154 - 0.174

1.486 - 1.660

Uniaxial (-)

Californite (Vesuvianite)

0.003 - 0.006

1.700 - 1.752

Uniaxial (+/-)

Canasite

0.009

1.534 - 1.543

Biaxial (-)

Cancrinite

0.012 - 0.025

1.495 - 1.528

Uniaxial (+/-)

Carnegieite

0.003 - 0.004

1.526 - 1.546

Uniaxial (-)

Carnelian (Chalcedony)

0.003 - 0.009

1.530 - 1.543

Uniaxial (+)

Cassiterite

0.103

1.990 - 2.100

Uniaxial (+)

Catapleiite

0.036

1.591 - 1.627

Biaxial (+)

Cavansite

0.009

1.542(2) - 1.551(2)

Biaxial (+)

Celadonite

0.027 - 0.030

1.579 - 1.661

Biaxial (-)

Celestine (Celestite)

0.011

1.619 - 1.632

Biaxial (+)

Ceruleite

0.020

1.600 - 1.620

Biaxial (?)

Cerussite

0.273

1.803 - 2.076

Biaxial (-)

Cervantite

0.100

2.000 - 2.100

Biaxial

Chabazite

0.002 - 0.006

1.478 - 1.493

Biaxial (+/-)

Chalcanthite

0.029

1.514 - 1.543

Biaxial (-)

Chalcedony

0.003 - 0.009

1.530 - 1.543

Uniaxial (+)

Chalcosiderite

0.069

1.775 - 1.844

Biaxial (-)

Chambersite

0.009

1.575 - 1.584

Biaxial (+)

Chamosite

0.070

1.600 - 1.670

Biaxial (-)

Charlesite

0.017

1.492 - 1.475

Uniaxial (-)

Charoite

0.009

1.550 - 1.559

Biaxial (+)

Chessylite (Azurite)

0.108

1.730 - 1.838

Biaxial (+)

Chevkinite-(Ce)

0.083

1.967 - 2.050

Biaxial (-)

Childrenite

0.027 - 0.042

1.644 - 1.691

Biaxial (-)

Chiastolite

0.007 - 0.013

1.627 - 1.645

Biaxial (-)

Chiquitanita (Chalcedony)

0.003 - 0.009

1.530 - 1.543

Uniaxial (+)

Chkalovite

0.005

1.544 - 1.549

Biaxial (+)

Chlorastrolite

0.014 - 0.016

1.674 - 1.764

Biaxial (+)

Chlorite (Chlinochlore)

0.005 - 0.011

1.571 - 1.599

Biaxial (+)

Chondrodite

0.027 - 0.032

1.592 - 1.675

Biaxial (+)

Chrome Diopside

0.024 - 0.030

1.668 - 1.703

Biaxial (+)

Chrome Tremolite

0.023 - 0.028

1.599 - 1.637

Biaxial (-)

Chromite

0 (Isotropic)

2.080 - 2.016

Isotropic

Chrysoberyl

0.010

1.746 - 1.756

Biaxial (+)

Chrysocolla

0.023 - 0.050

1.575 - 1.635

Biaxial (-)

Chrysoprase

0.004

1.530 - 1.543

Biaxial (+)

Chrysotile

0.001

1.569 - 1.570

Biaxial

Cinnabar

0.351

2.905 - 3.256

Uniaxial (+)

Citrine (Quartz)

0.009

1.543 - 1.554

Uniaxial (+)

Cleavelandite (Albite)

0.010

1.528 - 1.542

Biaxial (+)

Cleiophane (Sphalerite)

0 (Isotropic)

2.369

Isotropic

Clinochlore

0.005 - 0.011

1.571 - 1.599

Biaxial (+)

Clinohumite

0.028

1.623 - 1.728

Biaxial (+)

Clinozoisite

0.006 - 0.011

1.706 - 1.735

Biaxial (+)

Cobaltocalcite

0.255

1.855 - 1.600

Uniaxial (-)

Coffinite

1.730

1.730 - 1.750

Uniaxial (+/-)

Colemanite

0.028

1.586 - 1.614

Biaxial (+)

Conichalcite

0.023 - 0.046

1.778 - 1.846

Biaxial (+/-)

Connellite

0.014 - 0.026

1.724 - 1.758

Uniaxial (+)

Cookeite

0.017 - 0.024

1.572 - 1.600

Biaxial (+)

Coquimbite

0.009

1.539 - 1.548

Uniaxial (+)

Cordierite (Iolite)

0.011 - 0.018

1.527 - 1.578

Biaxial (-)

Cornetite

0.055

1.765 - 1.820

Biaxial (-)

Covellite

1.170

1.450 - 2.620

Uniaxial (+)

Crandallite

0.009 - 0.011

1.613 - 1.632

Uniaxial (+)

Creedite

0.024

1.461 - 1.485

Biaxial (-)

Cristobalite

0.003

1.478 - 1.484

Uniaxial (-)

Crocidolite (Riebeckite)

0.024

1.461 - 1.485

Biaxial (-)

Crocoite

0.370

2.290(2) - 2.660(2)

Biaxial (+)

Cryolite

0.001

1.339 - 1.340

Biaxial (-)

Cuprite

0 (Isotropic)

2.849

Isotropic

Cuproadamite

0.055

1.708 - 1.773

Biaxial (+/-)

Cuprosklodowskite

0.010 - 0.012

1.654 - 1.667

Biaxial (-)

Cyanotrichite

0.067

1.588 - 1.655

Biaxial (+)

Cymrite

0.010

1.611 - 1.621

Biaxial (-)

Cyprine (Vesuvianite)

0.003 - 0.006

1.703 - 1.752

Uniaxial (+/-)

Birefringence

RI values

Optics

Danalite

0 (Isotropic)

1.747 - 1.771

Isotropic

Danburite

0.006

1.627 - 1.639

Biaxial (+/-)

Datolite

0.044

1.626 - 1.670

Biaxial (-)

Demantoid

0 (Isotropic)

1.880 - 1.890

Isotropic

Descloizite

0.165

2.185 - 2.350

Biaxial (-)

Diaboleite

0.130

1.850 - 1.980

Uniaxial (-)

Diamond

0 (Isotropic)

2.435

Isotropic

Diaspore 

0.048

1.682 - 1.752

Biaxial (+)

Diopside

0.030

1.663 - 1.728

Biaxial (+)

Dioptase

0.052

1.652 - 1.710

Uniaxial (+)

Dolomite

0.179

1.679 - 1.503

Uniaxial (-)

Dravite (Tourmaline)

0.022 - 0.029

1.612 - 1.661

Uniaxial (-)

Dumortierite

0.027

1.659 - 1.692

Biaxial (-)

Dunilite (Olivine)

0.035 - 0.038

1.650 - 1.710

Biaxial (+)

Durangite

0.027

1.659 - 1.692

Biaxial (-)

Birefringence

RI values

Optics

Eitelite

0.155

1.450 - 1.605

Uniaxial (-)

Ekanite 

0.012

1.568 - 1.580

Uniaxial (-)

Elbaite (Tourmaline)

0.018 - 0.021

1.615 - 1.651

Uniaxial (-)

Emerald (Beryl)

0.004 - 0.010

1.565 - 1.602

Uniaxial (-)

Endlichite (Vanadinite)

0.066

2.350 - 2.416

Uniaxial (-)

Enstatite

0.009 - 0.011

1.650 - 1.679

Biaxial (+)

Eosphorite

0.029 - 0.035

1.628 - 1.679

Biaxial (-)

Epididymite

0.002

1.544 - 1.546

Biaxial (+)

Epidote

0.019 - 0.046

1.715 - 1.797

Biaxial (-)

Epistilbite

0.010

1.502 - 1.512

Biaxial (-)

Erythrite

0.073

1.626 - 1.701

Biaxial (+)

Esperite

0.012

1.762 - 1.774

Biaxial (-)

Ettringite

0.021

1.470 - 1.491

Uniaxial (-)

Euclase

0.019

1.652 - 1.671

Biaxial (+)

Eucryptite

0.013

1.570 - 1.587

Uniaxial (+)

Eudialyte

0.004

1.606 - 1.613

Uniaxial (+/-)

Euxenite-(Y)

0 (Isotropic)

2.060 - 2.240

Isotropic

Birefringence

RI values

Optics

Fassaite (Augite)

0.026 - 0.039

1.680 - 1.774

Biaxial (+)

Faustite

0

1.612

Biaxial (+)

Fayalite

0.042 - 0.051

1.731 - 1.875

Biaxial (-)

Ferberite

0.159

2.255 - 2.414

Biaxial (+)

Feldspar: Adularia

0.007 - 0.010

1.514 - 1.539

Biaxial (-)

Feldspar: Albite

0.010

1.528 - 1.542

Biaxial (+)

Feldspar: Andesine

0.010

1.528 - 1.542

Biaxial (+)

Feldspar: Anorthite

0.012 - 0.013

1.573 - 1.590

Biaxial (-)

Feldspar: Bytownite

0.010 - 0.011

1.563 - 1.583

Biaxial (+/-)

Feldspar: Hyalophane

0.005

1.542 - 1.547

Biaxial (-)

Feldspar: Labradorite

0.008 - 0.010

1.554 - 1.573

Biaxial (+)

Feldspar: Microcline

0.007 - 0.010

1.514 - 1.539

Biaxial (-)

Feldspar: Moonstone

0.006 - 0.007

1.518 - 1.527

Biaxial (-)

Feldspar: Oligoclase

0.010

1.538 - 1.550

Biaxial (-)

Feldspar: Orthoclase

0.004 - 0.005

1.518 - 1.525

Biaxial (-)

Feldspar: Sanidine

0.007

1.518 - 1.531

Biaxial (-)

Feldspar: Sunstone

0.007 - 0.010

1.525 - 1.552

Biaxial (-)

Feldspar: Valencianite

0.007 - 0.010

1.514 - 1.539

Biaxial (-)

Fergusonite-(Ce)

0.100

2.200 - 2.300

Uniaxial (-)

Ferri-Katophorite

0.020

1.640 - 1.692

Biaxial (-)

Ferro-Axinite

0.009 - 0.011

1.672 - 1.704

Biaxial (-)

Ferro-edenite

0.020

1.710 - 1.730

Biaxial (-)

Ferrotantalite

0.170

2.260 - 2.430

Biaxial (-)

Fluorapatite (Apatite)

0.004

1.631 - 1.646

Uniaxial (-)

Fluorbritholite-(Ce)

0.006

1.786 - 1.792

Uniaxial (-)

Fluorite 

0 (Isotropic)

1.433 - 1.448

Isotropic

Fluornatromicrolite 

0 (Isotropic)

2.030

Isotropic

Fluoro-potassic-hastingsite

0.030

1.668 - 1.698

Biaxial (-)

Forsterite

0.033 - 0.042

1.636 - 1.772

Biaxial (+)

Francevillite

0.195 - 0.217

1.752 - 2.002

Biaxial (-)

Franklinite

0 (Isotropic)

2.360(2)

Isotropic

Friedelite 

0.032 - 0.035

1.627 - 1.663

Uniaxial (-)

Fuchsite (Muscovite)

0.035 - 0.042

1.552 - 1.618

Biaxial (-)

Birefringence

RI values

Optics

Gadolinite-(Y)

0.050

1.770 - 1.820

Biaxial (+)

Gahnite

0 (Isotropic)

1.790 - 1.818

Isotropic

Ganophyllite

0.076

1.537 - 1.613

Biaxial (-)

Garnet: Almandine

0 (Isotropic)

1.830

Anomalously Biaxial

Garnet: Andradite

0 (Isotropic)

1.887

Isotropic

Garnet: Demantoid

0 (Isotropic)

1.880 - 1.890

Isotropic

Garnet: Grossular

0 (Isotropic)

1.731 - 1.754

Isotropic

Garnet: Hessonite

0 (Isotropic)

1.742 - 1.748

Isotropic

Garnet: Hydrogrossular

0 (Isotropic)

1.680 - 1.712

Isotropic

Garnet: Melanite

0 (Isotropic)

1.855 - 1.895

Isotropic

Garnet: Pyrope

0 (Isotropic)

1.720 - 1.756

Isotropic

Garnet: Rhodolite

0 (Isotropic)

1.760 +/-

Isotropic

Garnet: Rosolite

0 (Isotropic)

1.731 - 1.754

Isotropic

Garnet: Spessartine

0 (Isotropic)

1.789 - 1.820

Isotropic

Garnet: Topazolite

0 (Isotropic)

1.855 - 1.895

Isotropic

Garnet: Tsavorite

0 (Isotropic)

1.735 - 1.744

Isotropic

Garnet: Umbalite

0 (Isotropic)

1.735 - 1.744

Isotropic

Garnet: Uvarovite

0 (Isotropic)

1.865

Isotropic

Gaspeite

0.220

1.610 - 1.830

Uniaxial (-)

Gaudefroyite

0.210

1.805 - 2.020

Uniaxial (+)

Gaylussite

0.079

1.444 - 1.523

Biaxial (-)

Genthelvite

0 (Isotropic)

1.738 - 1.752

Isotropic

Gilalite

0.075

1.560 - 1.635

Biaxial (-)

Glauberite

0.022

1.507 - 1.536

Biaxial (-)

Gmelinite-Na

0.002 - 0.014

1.476 - 1.494

Uniaxial (+/-)

Golden Beryl (Heliodor)

0.005 - 0.009

1.566 - 1.579

Uniaxial (-)

Goosecreekite

0.007

1.495 - 1.502

Biaxial (-)

Görgeyite

0.024

1.560 - 1.584

Biaxial (+)

Gormanite

0.041

1.619 - 1.660

Biaxial (-)

Goshenite (Beryl)

0.003 - 0.010

1.562 - 1.615

Uniaxial (-)

Graftonite

0.024 - 0.027

1.695 - 1.736

Biaxial (+)

Grandidierite

0.033 - 0.037

1.590 - 1.639

Biaxial (-)

Greenlandite (Fuchsite)

0.035 - 0.042

1.552 - 1.618

Biaxial (-)

Grossular (Garnet)

0 (Isotropic)

1.731 - 1.754

Isotropic

Gypsum

0.010

1.519 - 1.530

Biaxial (+)

Gyrolite

0.014

1.535 - 1.549

Biaxial (-)

Birefringence

RI values

Optics

Hackmanite

0 (Isotropic)

1.483 - 1.487

Isotropic

Halite

0 (Isotropic)

1.5443

Isotropic

Hambergite

0.074

1.554 - 1.631

Biaxial (+)

Hanksite

0.020

1.461 - 1.481

Uniaxial (-)

Hardystonite

0.011

1.661 - 1.672

Uniaxial (-)

Hauerite

0 (Isotropic)

2.690

Isotropic

Haüyne

0 (Isotropic)

1.494 - 1.509

Isotropic

Hedenbergite

0.029

1.669 - 1.757

Biaxial (+)

Heliodor (Beryl)

0.005 - 0.009

1.566 - 1.579

Uniaxial (-)

Helvine

0 (Isotropic)

1.728 - 1.749

Isotropic

Helvite (Helvine)

0 (Isotropic)

1.728 - 1.749

Isotropic

Hematite

0.280

2.870 - 3.220

Uniaxial (-)

Hemimorphite

0.022

1.614 - 1.636

Biaxial (+)

Henmilite

0.030

1.585 - 1.615

Biaxial (-)

Herderite

0.033

1.556 - 1.620

Biaxial (-)

Hessonite (Garnet)

0 (Isotropic)

1.742 - 1.748

Isotropic

Heulandite

0.009

1.491 - 1.512

Biaxial (+)

Hexagonite (Tremolite)

0.023 - 0.028

1.599 - 1.637

Biaxial (-)

Hibonite

0.017

1.790 - 1.807

Uniaxial (-)

Hiddenite (Spodumene)

0.014 - 0.016

1.657 - 1.681

Biaxial (+)

Hodgkinsonite

0.026

1.720 - 1.746

Biaxial (-)

Hopeite

0.018

1.572 - 1.592

Biaxial (-)

Howlite

0.017

1.583 - 1.600

Biaxial (-)

Hübnerite 

0.130

2.170 - 2.320

Biaxial (+)

Humite

0.032

1.607 - 1.675

Biaxial (+)

Hureaulite

0.012 - 0.015

1.637 - 1.671

Biaxial (-)

Hyalite (Opal)

0 (Isotropic)

1.440 - 1.460

Isotropic

Hyalophane (Microcline)

0.005

1.542 - 1.547

Biaxial (-)

Hydroboracite

0.049

1.520 - 1.571

Biaxial (+)

Hydrogrossular (Garnet)

0 (Isotropic)

1.680 - 1.712

Isotropic

Hydrohetaerolite

0.160

2.102 - 2.262

Uniaxial (-)

Hydroxylherderite

0.029 - 0.030

1.589 - 1.643

Biaxial (-)

Hydrozincite

0.120

1.630 - 1.750

Biaxial (-)

Hypersthene

0.011 - 0.018

1.669 - 1.773

Biaxial (-)

Birefringence

RI values

Optics

Idocrase (Vesuvianite)

0.003 - 0.006

1.703 - 1.752

Uniaxial (+/-)

Ilvaite

0.156

1.727 - 1.883

Biaxial (+)

Inderborite

0.048

1.482 - 1.530

Biaxial (-)

Inderite

0.017

1.488 - 1.505

Biaxial (+)

Indicolite (Tourmaline)

0.014 - 0.040

1.614 - 1.666

Uniaxial (-)

Inyoite

0.025

1.495 - 1.520

Biaxial (-)

Iolite (Cordierite)

0.011 - 0.018

1.527 - 1.578

Biaxial (-)

Birefringence

RI values

Optics

Jadeite

0.017

1.488 - 1.505

Biaxial (+)

Jamesonite

0.022

1.635 - 1.663

Biaxial (-)

Jeremejevite

0.013

1.640 - 1.653

Uniaxial (-)

Jet

0 (Isotropic)

1.440 - 1.460

Isotropic

Johachidolite

0.014

1.712 - 1.726

Biaxial (+)

Johannsenite

0.029

1.703 - 1.745

Biaxial (+)

Johnsenite-(Ce)

0.011

1.637 - 1.648

Uniaxial (-)

Birefringence

RI values

Optics

Kaersutite

0.030 - 0.083

1.670 - 1.772

Biaxial (-)

Kaliborite

0.042

1.508 - 1.550

Biaxial (+)

Kämmererite

0.003

1.571 - 1.597

Biaxial (+/-)

Kaolinite

0.007 - 0.017

1.553 - 1.570

Biaxial (-)

Katophorite

0.020

1.640 - 1.692

Biaxial (-)

Kentbrooksite

0.005

1.623 - 1.628

Uniaxial (-)

Kernite

0.034

1.454 - 1.488

Biaxial (-)

Kinoite

0.038

1.638 - 1.676

Biaxial (-)

Kolwezite

0.212

1.688 - 1.900

Biaxial (-)

Korite

0.150

1.520 - 1.670

Kornerupine

0.014

1.660 - 1.684

Biaxial (-)

Kovdorskite

0.022

1.527 - 1.549

Biaxial (-)

Kröhnite

0.057

1.544 - 1.601

Biaxial (-)

Kulanite

0.020

1.703 - 1.723

Biaxial (+)

Kunzite (Spodumene)

0.014 - 0.016

1.657 - 1.681

Biaxial (+)

Kurchatovite

0.063

1.635 - 1.698

Biaxial (-)

Kurnakovite

0.027 - 0.034

1.488 - 1.525

Biaxial (-)

Kutnohorite

0.191 - 0.0192

1.519 - 1.727

Uniaxial (-)

Kyanite 

0.015 - 0.016

1.712 - 1.734

Biaxial (-)

Birefringence

RI values

Optics

Labradorite

0.008 - 0.010

1.554 - 1.573

Biaxial (+)

Lapis Lazuli

0 (Isotropic)

1.500 - 1.670

Isotropic

Larimar (Pectolite)

0.037

1.594 - 1.642

Biaxial (+)

Laumontite

0.012

1.502 - 1.525

Biaxial (-)

Lawsonite

0.019 - 0.021

1.665 - 1.686

Biaxial (+)

Lazulite

0.033 - 0.037

1.604 - 1.663

Biaxial (-)

Lazurite

0 (Isotropic)

1.502 - 1.522

Isotropic

Leadhillite

0.140

1.870 - 2.010

Biaxial (-)

Legrandite

0.060 - 0.066

1.675 - 1.740

Biaxial (+)

Leifite

0.011

1.511 - 1.522

Uniaxial (+)

Lepidocrocite

0.570

1.940 - 2.510

Biaxial (-)

Lepidolite

0.018 - 0.038

1.525 - 1.587

Biaxial (-)

Leucite 

0.001

1.508 - 1.509

Uniaxial (+)

Leucophanite

0.027

1.571 - 1.598

Biaxial (-)

Leucophoenicite

0.031

1.751 - 1.782

Biaxial (-)

Libyan Desert Glass

-

1.460 - 1.465

-

Liddicoatite 

0.016

1.621 - 1.637

Uniaxial (-)

Linarite

0.050

1.809 - 1.859

Biaxial (-)

Lithiopilite

0.008 - 0.010

1.663 - 1.691

Biaxial (+)

Lizardite 

0.012

1.541 - 1.568

Biaxial (-)

Londonite

0 (Isotropic)

1.6935 - 1.694

Isotropic

Lorenzenite

0.120

1.910 - 2.060

Biaxial (-)

Ludlamite 

0.038 - 0.044

1.650 - 1.697

Biaxial (+)

Ludwigite

0.110 - 0.170

1.830 - 2.020

Biaxial (+)

Birefringence

RI values

Optics

MacFallite

0.037 - 0.040

1.773 - 1.815

Biaxial (-)

Magnesio-Axinite

0.009 - 0.011

1.672 - 1.704

Biaxial (-)

Magnesio-Riebeckite

0.012

1.668 - 1.680

Biaxial (-)

Magnesiotaaffeite-2N'2S

0.055

1.722 - 1.777

Uniaxial (+)

Magnesiotaaffeite-6N'3S

0.004

1.735 - 1.739

Uniaxial (-)

Magnesite

0.191

1.509 - 1.700

Uniaxial (-)

Magnetite

0 (Isotropic)

2.420

Isotropic

Malachite

0.254

1.655 - 1.909

Biaxial (-)

Mandarin Garnet (Spessartine)

0 (Isotropic)

1.789 - 1.820

Isotropic

Manganite

0.028

2.250 - 2.530

Biaxial (+)

Manganoan Adamite

0.055

1.708 - 1.773

Biaxial (+/-)

Manganotantalite

0.200

2.140 - 2.340

Biaxial (+)

Mansfieldite

0.020 - 0.032

1.622 - 1.663

Biaxial (+)

Marialite

0.007 - 0.009

1.532 - 1.550

Uniaxial (-)

Maw-sit-sit

0.015

1.760 - 1.781

Biaxial

Meionite

0.034 - 0.038

1.556 - 1.600

Uniaxial (-)

Melanite

0 (Isotropic)

1.855 - 1.895

Isotropic

Melanterite

0.016

1.470 - 1.486

Biaxial (+)

Meliphanite

0.019

1.592 - 1.672

Uniaxial (-)

Mellite

0.028

1.511 - 1.539

Uniaxial (-)

Meta-Autunite

0.015 - 0.023

1.584 - 1.630

Uniaxial (-)

Meyerhofferite

0.060

1.500 - 1.560

Biaxial (-)

Microcline

0.007 - 0.010

1.514 - 1.539

Biaxial (-)

Microlite

0 (Isotropic)

1.993 - 2.020

Isotropic

Milarite

0.003

1.529 - 1.551

Uniaxial (-)

Mimetite

0.019

2.128 - 2.147

Uniaxial (-)

Moldavite

0 (Isotropic)

1.480 - 1.540

Isotropic

Monazite

0.053 - 0.067

1.770 - 1.860

Biaxial (+)

Montebrasite

0.022 - 0.030

1.594 - 1.645

Biaxial (+/-)

Montgomeryite

0.010

1.572 - 1.582

Biaxial (-)

Montmorillonite

0.020

1.485 - 1.550

Biaxial (-)

Moonstone (Feldspar)

0.006 - 0.007

1.518 - 1.527

Biaxial (-)

Mordenite

0.005

1.472 - 1.487

Biaxial (+/-)

Morganite (Beryl)

0.005 - 0.009

1.573 - 1.600

Uniaxial (-)

Morion (Quartz)

0.009

1.544 - 1.553

Uniaxial (+)