Tourmaline Education

     

     

     
    GENERAL DESCRIPTION

     

    • Name: Tourmaline is derived of the word “tourmali”, this word in singhalese  was used for colored gems, mostly zircons.
        • Formula: Tourmaline is the name for a group of related mineral species, with a very complex chemical composition. 
        • Chromdravite: NaMg3[Cr,Fe3+]6(BO3)3Si6O18(OH)4
        • Buergerite: NaFe3+3Al6(BO3)3Si6O18(O)3(OH)
        • Dravite: NaMg3Al6(BO3)3Si6O18(OH)4
        • Elbaite: Na(Li1.5Al1.5)Al6(BO3)3Si6O18(OH)4
        • Feruvite: CaFe2+3[Al5Mg](BO3)3Si6O18(OH)4
        • Foitite: [Fe2+2(Al,Fe3+)]Al6(BO3)3Si6O18(OH)4
        • Liddicoatite: Ca(Li2Al)Al6(BO3)3Si6O18(OH)4
        • Magnesiofoitite, Olenite, Rossmanite, Schorl, Uvite, Povondraite, Bosiite, ...
        • Common Impurities:  Na, Li, Ca, Mn, Mg, Fe, Cr, Vn, Cu, Ti, F.
          • Green - Blue: Fe, Ti.
          • Red, Pink, Yellow: Mn
          • Paraiba, Pink: Cu
        • Crystal system: trigonal.
        • Habit: Prismatic to acicular crystals.
        • Borosilicates of the cyclosilicate superclass 
          • Genesis:  Pegmatites,  Magamatique, Metamorphic, Hydrothermal. Tourmaline is located in granitic igneous rocks and pegmatitic. Also in metamorphic rocks and specifically in schists and marbles . 
          • Origen: Tourmaline is found: Afghanistan, Brazil, Burma (Myanmar), China, India, Kenia, Madagascar, Mozambique, Namibia, Nepal, Nigeria, Pakistan, Russia, Sri Lanka, Tanzania, USA, Vietnam, Zambia, Zimbabwe …

          Two-phase trichites inclusions  Rubellite

           

           

           

          Growth tubes and fractures Rubellite

           

           

           

          Solid Inclusions Rubellite


          PHYSICAL AND OPTICAL PROPERTIES OF TOURMALINE

           

          • Hardness (Mohs): 7 - 7½ 
          • Fracture: Sub-Conchoidal, Irregular.
          • Colour: All. Multicolored, Bicolor, Red, Orange, Yellow, Green, Blue, Purple, Violet, Brown, Neon Blue, Colorless, sometimes Asterism, Change Color and Trapiche.
            • Achroite - Colorless
            • Bicolor - two or more colors.
            • Canary - bright yellow
            • Chrome - intense green colored by Cr or Vn
            • Indicolite - blue
            • Rubellite - pink - red 
            • Paraiba - intense blue - green colored by Cu (Paraiba, Mozambique)
            • Verdelite  - green gem
            • Watermelon – pink in the center, green around
          • Transparency: Transparent, translucent, opaque.
          • Streak: White.
          • Lustre: Vitreous
          • Dispersion: 0,017
          • Density: 2.85 to 3.35 g/cm3
          • Optic nature: Uniaxial negative
          • Refractive index:  1.616 - 1.666
          • Birefringence: 0.014 to 0.040  (usually 0.020). 
          • Pleochroism: Light to Strong (when the ordinary ray having a dark color).  
          • Fluorescence: Mostly inert
          • Absorption spectrum: Variable- according color and/or tourmaline.
          • Pyroelectric and piezoelectric
          • Inclusions:  Interconnected two-phase inclusions typical for tourmaline ("trichite"),   film-like liquid inclusions, parallel oriented hollow tubes, needle-like mineral inclusions, fractures. Paraiba, red and pink tourmalines will show eye-visible inclusions
          • Enhancements:
            • Irradiation
            • Heat Treatment
            • Fracture filling (oiled, etc..)

           

          Healed fractures appearance frosty (Paraiba treated) 

           

           

          Two - phases inclusions. Trichites.

           

           

          Two-phases inclusions. Trichites. Colored growth tubes. Rubellite

           

           

           Growth tubes Rubellite 

           

          Two-phases inclusions. Needles. Bicolor tourmaline.

           

          Colored growth tubes. Two-phases inclusions. Trichites. Healed fractures