Tourmaline
Tourmaline (tur-mah-Leen) is a crystal boron silicate meeneral compoondit wi elements sic as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is clessifee'd 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 applee'd tae different gemstanes foond in Sri Lanka.
| Tourmaline | |
|---|---|
 Schorl Tourmaline | |
| General | |
| Category | Cyclosilicate |
| Formula (repeatin 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] |
| Creestal seestem | Trigonal |
| Identification | |
| Colour | Maist commonly black, but can range frae broun, violet, green, pink, or in a dual-colored pink an green. |
| Creestal habit | Parallel an elongatit. Acicular prisms, whiles radiatin. Massive. Scattered grains (in granite). |
| Cleavage | Indistinct |
| Fractur | Uneven, smaa conchoidal, brickle |
| Mohs scale haurdness | 7–7.5 |
| Skinkle | Vitreous, whiles resinous |
| Streak | White |
| Speceefic gravity | 3.06 (+.20 -.06)[1] |
| Density | 2.82–3.32 |
| Polish skinkle | 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; teepically about .020 but in dark stones it may reak .040[1] |
| Pleochroism | teepically moderate tae strang[1] Reid Tourmaline: Definite; dark reid,licht reid Green Tourmaline: Strang; dark green, yellae-green Broun Tourmaline: Definite; dark broun, licht broun Blue Tourmaline: Strang; dark blae, licht blae |
| Dispersion | .017[1] |
| Ultraviolet fluorescence | pink stanes—inert tae vera waik reid tae violet in lang an short wave[1] |
| Absorption spectra | a strang narra band at 498 nm, an naur complete absorption o reid doun tae 640nm in blae an green stanes; reid an pink stanes shaw lines at 458 an 451nm as weel as a braid band in the green spectrum[1] |
References
eedit- ↑ a b c d e f g h i Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN 0-87311-019-6
- ↑ Mindat tourmaline group Accessed September 12, 2005. This website details specifically and clearly how the complicated chemical formula is structured.