Properties of Commonly Faceted Minerals and Materials

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 isometric   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


Perfect Transfer Index

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Bob Keller