Tourmaline

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Tourmaline
TourmalineUSGOV.jpg
Schorl Tourmaline
General
Category Cyclosilicate
Formula
(repeating unit)
(Ca,K,Na,[])(Al,Fe,Li,Mg,Mn)3(Al,Cr, Fe,V)6
(BO3)3(Si,Al,B)6O18(OH,F)4
[1][2]
Identification
Color Maist commonly black, but can range frae broun, violet, green, pink, or in a dual-colored pink an green.
Crystal habit Parallel an elongatit. Acicular prisms, sometimes radiatin. Massive. Scattered grains (in granite).
Crystal seestem Trigonal
Cleavage Indistinct
Fractur Uneven, smaa conchoidal, brittle
Mohs scale hairdness 7–7.5
Luster Vitreous, sometimes resinous
Streak White
Specific gravity 3.06 (+.20 -.06)[1]
Density 2.82–3.32
Polish luster Vitreous[1]
Optical properties Double refractive, uniaxial negative[1]
Refractive index nω=1.635–1.675, nε=1.610–1.650
Birefringence -0.018 to -0.040; typically about .020 but in dark stones it may reach .040[1]
Pleochroism typically moderate tae strang[1]
Reid Tourmaline: Definite; dark reid,licht reid
Green Tourmaline: Strong; dark green, yellae-green
Broun Tourmaline: Definite; dark broun, licht broun
Blue Tourmaline: Strang; dark blue, licht blue
Dispersion .017[1]
Ultraviolet fluorescence pink stanes—inert tae very weak reid tae violet in long an short wave[1]
Absorption spectra a strang narrow band at 498 nm, an almaist complete absorption o reid doun tae 640nm in blue an green stanes; reid an pink stanes shaw lines at 458 an 451nm as well as a broad band in the green spectrum[1]

Tourmaline (tur-mah-Leen) is a crystal boron silicate mineral compoondit wi elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is classified as a semi-precious stane an the gemstane comes in a wide variety o colours. The name comes frae the Sinhalese wird "Thuramali" (තුරමලි) or "Thoramalli" (තෝරමල්ලි), which applied tae different gemstanes foond in Sri Lanka.

References[eedit | eedit soorce]

  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN 0-87311-019-6
  2. Mindat tourmaline group Accessed September 12, 2005. This website details specifically and clearly how the complicated chemical formula is structured.