Archive for the Natural Gemstones Category

  • Star Sapphire

    Refractive Index : 1.770 – 1.762 (+0.009 – 0.005)

    Optical Characteristic : DR U-, AGG

    Specific Gravity : 4.00 (+0.10 – 0.05)

    Formula : AI2O3

    Crystal System : Trigonal

    Variety/Species : Sapphire

    Species/Group : Corundum

    Birefringence : 0.008 to 0.010

    Dispersion : 0.018

    Hardness : 9

    Toughness : Good to excellent

    Ultrasonic : Usually safe

    Steam : usually safe

    UV Long : Inert to strong

    UV Short : Inert [...]

  • Star spinel

    Refractive Index : 1.718 (+0.017 – 0.008)

    Optical Characteristic : SR

    Specific Gravity : 3.60 (+0.10 – 0.03)

    Formula : MgAI2O4

    Crystal System : Cubic

    Variety/Species : spinel

    Species/Group : Spinel Group

    Birefringence : none

    Dispersion : 0.020

    Hardness : 8

    Toughness : good

    Ultrasonic : Usually safe

    Steam : usually safe

    UV Long : Inert to strong

    UV Short : Inert to weak

    Pleochroism : None

    Strength : N/A

    Pleochroism Colors [...]

  • Tourmaline Group

    Refractive Index : 1.644 – 1.624 + 0.134 – 0.021

    Optical Characteristic : DR U-

    Specific Gravity : 3.06 + 0.20 – 0.06

    Formula : Na(Li,AI)3AI6(BO3)3Si6018(OH)4

    Crystal System : Trigonal

    Variety/Species : All

    Species/Group : Tourmaline Group

    Birefringence : 0.018 to 0.040

    Dispersion : 0.017

    Hardness : 7 to 7.5

    Toughness : Fair

    Ultrasonic : Risky

    Steam : Risky

    UV Long : Inert to weak

    UV Short : Inert [...]

  • Sphalerite

    Refractive Index : 2.50 – 2.369

    Optical Characteristic : SR

    Specific Gravity : 4.05 (+0.05 – 0.15)

    Formula : ZnS + Fe

    Crystal System : Cubic

    Variety/Species : Sphalerite

    Species/Group : sphalerite Group

    Birefringence : none

    Dispersion : 0.156

    Hardness : 3.5 to 4

    Toughness : poor

    Ultrasonic : Never

    Steam : Never

    UV Long : Inert to strong

    UV Short : Inert to strong

    Pleochroism : None

    Strength : N/A

    Pleochroism [...]

  • Spodumene

    Refractive Index : 1.676 – 1.662 (+0.005 – 0.005)

    Optical Characteristic : DR, B+

    Specific Gravity : 3.18 (+0.03 – 0.03)

    Formula : LiAISi2O6

    Crystal System : Monoclinic

    Variety/Species : spodumene

    Species/Group : Pyroxene group

    Birefringence : 0.014

    Dispersion : 0.017

    Hardness : 6.5 to 7

    Toughness : poor

    Ultrasonic : Never

    Steam : Never

    UV Long : Inert

    UV Short : Inert

    Pleochroism : 2 colors

    Strength : moderate

    Pleochroism Colors [...]

  • Sphene

    Refractive Index : 2.034 – 1.900 (+0.020 – 0.020)

    Optical Characteristic : DR, B+

    Specific Gravity : 3.52 (+0.02 – 0.02)

    Formula : CaTiSiO5

    Crystal System : Monoclinic

    Variety/Species : All

    Species/Group : sphene

    Birefringence : 0.100 to 0.135

    Dispersion : 0.051

    Hardness : 5 to 5.5

    Toughness : Fair to poor

    Ultrasonic : risky

    Steam : Never

    UV Long : Inert

    UV Short : Inert

    Pleochroism : 3 colors

    Strength [...]

  • Sogdianite

    Refractive Index : 1608 – 1.606

    Optical Characteristic : DR, U-

    Specific Gravity : 2.90 – 2.76

    Formula : (K,Na)2Li,Fe,AI,Ti)2Zr2(Si2O5)6

    Crystal System : Hexagonal

    Variety/Species : sogdianite

    Species/Group : Osumilite group

    Birefringence : 0.002

    Dispersion :

    Hardness : 5 to 7

    Toughness : poor

    Ultrasonic : Never

    Steam : Never

    UV Long : Inert to weak

    UV Short : Inert to weak

    Pleochroism : None

    Strength : N/A

    Pleochroism Colors : [...]

  • Spurrite

    Refractive Index : 1.679 – 1.640

    Optical Characteristic : DR, B-

    Specific Gravity : 3.00

    Formula : Ca5(SiO4)2(CO3)

    Crystal System : Monoclinic

    Variety/Species : All

    Species/Group : spurrite

    Birefringence : 0.039

    Dispersion :

    Hardness : 5

    Toughness : poor

    Ultrasonic : Never

    Steam : Never

    UV Long : Inert

    UV Short : Inert

    Pleochroism : None

    Strength : N/A

    Pleochroism Colors : None

    Heat : sensitive

    Acids : sensitive

    Light : stable

    Polish Luster : [...]

  • Staurolite

    Refractive Index : 1.746 – 1.736 (+0.015 – 0.015)

    Optical Characteristic : DR, B+, AGG

    Specific Gravity : 3.71 (+0.08 -0.06)

    Formula : (Fe++,Mg)2AI9(Si,AI)4O20(O,OH)4

    Crystal System : Monoclinic

    Variety/Species : All

    Species/Group : staurolite

    Birefringence : 0.009 to 0.015

    Dispersion : 0.021

    Hardness : 7 to 7.5

    Toughness : fair

    Ultrasonic : risky

    Steam : risky

    UV Long : Inert

    UV Short : Inert

    Pleochroism : 3 colors

    Strength : moderate

    Pleochroism [...]

  • Stibiotantalite

    Refractive Index : 2.460 – 2.370

    Optical Characteristic : DR, B+

    Specific Gravity : 7.46 – 7.34

    Formula : SbTaO4

    Crystal System : Orthorhombic

    Variety/Species : All

    Species/Group : stibiotantalite

    Birefringence : 0.090

    Dispersion : 0.146

    Hardness : 5 to 5.5

    Toughness : poor

    Ultrasonic : Never

    Steam : Never

    UV Long : Inert

    UV Short : Inert

    Pleochroism : None

    Strength : N/A

    Pleochroism Colors : None

    Heat : sensitive

    Acids : sensitive

    Light [...]