| Material | Refractive Index |
Critical Angle |
Birefringenge | Dispersion | Hardness | Specific Gravity |
Crystal System |
Class | Formula | Cleavage |
| Apatite series | 1.64 | 37.57° | .004 | .013 | 5.0 | 3.05-3.20 | hexagonal | 6/m | Ca5(PO4,CO3)3(F,Cl,OH) | 2; {0001}indistinct; {10-10} trace |
| Beryl | 1.57-1.60 | 38.68-39.56° | .006-.009 | .014 | 7.5-8.0 | 2.60-2.90 | hexagonal | 6/m 2/m 2/m | Be3Al2Si6O18 | 1; {0001} indistinct |
| Color varieties of beryl include aquamarine (blue), emerald (green), goshenite (colorless), heliodor (yellow) and morganite (pink). | ||||||||||
| Chrysoberyl | 1.75 | 34.85° | .010 | .015 | 8.5 | 3.75 | orthorhombic | 2/m 2/m 2/m | BeAl2O4 | 3; {110} distinct, {010} imperfect, {001} indistinct |
| Corundum | 1.77 | 34.40° | .008 | .018 | 9.0 | 4.00-4.10 | hexagonal | B3 2/m | Al2O3 | 2; {0001} and {10-11} parting |
| Ruby is red corundum. All other colors of corundum are classified as sapphires. | ||||||||||
| Cubic Zirconia | 2.15-2.18 | 27.30-27.72° | .000 | .058-.060 | 8.3-8.5 | 5.6-6.0 | cubic | ZrO2 | ||
| Danburite | 1.63 | 37.84° | .006 | .016 | 7.0 | 2.97-3.02 | orthorhombic | 2/m 2/m 2/m | CaB2(SiO4)2 | 1; {001} indistinct |
| Diamond | 2.41 | 24.52° | .000 | .044 | 10.0 | 3.51 | isometric | 4/m B3 2/m | C | 1; {111} perfect |
| Epidote | 1.75 | 34.85° | .047 | .030 | 6.0-7.0 | 3.35-3.50 | monoclinic | 2m | Ca2(Fe,Al)3(Si2O7)(SiO4)(O,OH_2 | 6; {001} and {010} perfect, {100}, {110}, {-110} and {-201} partings |
| Feldspar Group |
1.52-1.58 | 39.23-41.12° | .007-.013 | .012 | ||||||
| – orthoclase | ~ | ~ | ~ | ~ | 6.0-6.5 | 2.55-2.63 | monoclinic | 2m | KAlSi3O8 | 2; {11-20} and {10-11} indistinct |
| – labradorite | ~ | ~ | ~ | ~ | 6.0-6.5 | 2.69-2.72 | triclinic | B1 | Na.5-.3Ca.5-.7Al1.5-1.7Si2.5-2.3)8 | 3; {001} perfect, {010} and {110} nearly perfect |
| – Sunstone (oligoclase) | ~ | ~ | ~ | ~ | 6.0-6.5 | 2.63-2.67 | triclinic | B1 | 70-90%(Na,Ca)Al(Al,Si)Si2O810-30%CaAl2Si2O8 | 3; {001} perfect, {010} nearly perfect, {110} imperfect |
| Fluorite | 1.43 | 44.37° | .000 | .007 | 4.0 | 3.218 | isometirc | 4/m B3 2/m | CaF2 | 1; {111} perfect |
| Garnet Group | ||||||||||
| – almandine | 1.78-1.81 | 33.54-34.18° | .000 | .024 | 7.0-7.5 | 4.10-4.30 | isometric | 4/m B3 2/m | Fe3Al2(SiO4)3 | 1; {110} parting sometimes distinct |
| – andradite | 1.85-1.89 | 31.94-32.74° | .000 | .057 | 6.5-7.0 | 3.70-4.10 | isometric | 4/m B3 2/m | Ca3Fe2(SiO4)3 | |
| – grossular | 1.73-1.74 | 35.08-35.31° | .000 | .027 | 6.5-6.7 | 3.40-3.60 | isometric | 4/m B3 2/m | Ca3Al2(SiO4)3 | 1; {110} parting |
| – pyrope | 1.73-1.76 | 34.62-35.31° | .000 | .022 | 7.0-7.5 | 3.50-3.80 | isometric | 4/m B3 2/m | Mg3Al2(SiO4)3 | 1; {110} parting sometimes distinct |
| – spessartine | 1.79-1.81 | 33.54-33.96° | .000 | .027 | 7.0-7.5 | 3.80-4.25 | isometric | 4/m B3 2/m | Mn3Al2(SiO4)3 | 1; {110} parting sometimes distinct |
| – uvarovite | 1.87 | 32.33° | .000 | 6.5-7.0 | 3.40-3.80 | isometric | 4/m B3 2/m | Ca3Cr2(SiO4)3 | ||
| Glass | 1.44-1.68 | 36.53-43.98° | 4.0-7.0 | 2.2-5.0 | (amorphous) | higly variable | ||||
| Iolite (cordierite) | 1.55 | 40.18° | .017 | .017 | 7.0-7.5 | 2.53-2.78 | orthorhombic | 2/m 2/m 2/m | Mg2Al4Si5O18 | 3; {010} distinct, {001} and {100} indistinct |
| Opal | 1.45 | 43.60° | .000 | 5.5-6.5 | 1.99-2.25 | (amorphous) | SiO2(nH20) | |||
| Peridot (forsterite) | 1.67 | 36.78° | .038 | .020 | 7.0 | 3.28 | orthorhombic | 2/m 2/m 2/m | Mg2SiO4 | 2; {010} and {100} imperfect |
| Quartz | 1.54 | 40.49° | .009 | .013 | 7.0 | 2.66 | hexagonal | 32 | SiO2 | 7; {10-11}{01-11}{10-10}{0001}{11-20}{11-21}{51-61} indistinct |
| Scapolite series | 1.58 | 39.27° | .022 | 5.5-6.0 | 2.50-2.78 | tetragonal | 4/m | (Na,Ca)4Al3Si9O24Cl | 2; {100} and {110} distinct | |
| Sphene (titanite) | 1.99-2.03 | 29.51-30.17° | .051 | .051 | 5.0-5.5 | 3.45-3.55 | monoclinc | 2/m | CaTiSiO5 | 2; {110} distinct, {221} parting |
| Spinel | 1.72 | 35.55° | .000 | .020 | 7.5-8.0 | 3.58 | orthorhombic | 4/m B3 2/m | MgAl2O4 | 1; {111} parting indistinct |
| Tanzanite (zoisite) | 1.70 | 36.03° | .006 | .030 | 6.5-7.0 | 3.55 | orthorhombic | 2/m 2/m 2/m | Ca2Al3(SiO4)3(OH) | 2; {100} perfect, {010} imperfect |
| Topaz | 1.61 | 38.40° | .008 | .014 | 8.0 | 3.49-3.57 | orthorhombic | 2/m 2/m 2/m | Al2SiO4(F,OH)2 | 1; {001} perfect |
| Tourmaline Group |
1.62-1.65 | 37.31-38.40° | .014-.044 | .017 | ||||||
| – dravite | ~ | ~ | ~ | ~ | 7.0 | 3.03 | hexagonal | 3m | NaMg3Al6(BO3)3Si6O18(OH)4 | 2; {11-20} and {10-11} indistinct |
| – elbaite | ~ | ~ | ~ | ~ | 7.0 | 3.03-3.10 | hexagonal | 3m | Na(Li,Al)3Al6(BO3)3Si6O18(OH)4 | 2; {11-20} and {10-11} indistinct |
| – liddicoatite | ~ | ~ | ~ | ~ | 7.5 | 3.02 | hexagonal | 3m | Ca(Li,Al)3Al6(BO3)3Si6O18(O,OH,F)4 | |
| – uvite | ~ | ~ | ~ | ~ | 7.5 | 3.04 | hexagonal | 3m | (Ca,Na)(Mg,Fe)3Al5Mg(BO3)3Si6O18(OH,F)4 | |
| Zircon | 1.94 | 31.03° | .060 | .038 | 7.5 | 4.60-4.70 | tetragonal | 4/m 2/m 2/m | ZrSiO4 | 2; {110} imperfect; {111} poor |