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Tourmaline
| 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] |
| IMA symbol | Tur[3] |
| Crystal system | Trigonal |
| Crystal class | Ditrigonal pyramidal (3m) H-M symbol: (3m) |
| Space group | R3m (no. 160) |
| Identification | |
| Color | Most commonly black, but can range from colorless to brown, red, orange, yellow, green, blue, violet, pink, or hues in-between. It can also be bi-colored, or even tri-colored. Rarely, it can be found as neon green or electric blue. |
| Crystal habit | Parallel and elongated; acicular prisms, sometimes radiating; massive; scattered grains (in granite) |
| Cleavage | Indistinct |
| Fracture | Uneven, small conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 7.0–7.5 |
| Luster | Vitreous, sometimes resinous |
| Streak | White |
| Diaphaneity | Translucent to opaque |
| Specific gravity | 3.06+0.20–0.06[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 −0.020 but in dark stones it may reach −0.040[1] |
| Pleochroism |
|
| Dispersion | 0.017[1] |
| Ultraviolet fluorescence | Pink stones; inert to very weak red to violet in long and short wave[1] |
| Absorption spectra | Strong narrow band at 498 nm, and almost complete absorption of red down to 640 nm in blue and green stones; red and pink stones show lines at 458 and 451 nm, as well as a broad band in the green spectrum[1] |
Tourmaline (/ˈtʊərməlɪn, -ˌliːn/ TOOR-mə-lin, -leen) is a crystalline silicate mineral group in which boron is compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. This gemstone comes in a wide variety of colors.
The name is derived from the Sinhalese tōramalli (ටෝරමල්ලි), which refers to the carnelian gemstones.[4]
- ^ a b c d e f g h i GIA Gem Reference Guide. Gemological Institute of America. 1995. ISBN 0-87311-019-6.
- ^ "Tourmaline". Mindat.org. Archived from the original on 2005-12-28. Retrieved 2005-09-12. This website details specifically and clearly how the complicated chemical formula is structured.
{{cite web}}: CS1 maint: postscript (link) - ^ Warr, L. N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ "tourmaline". Oxford Dictionaries. Archived from the original on October 16, 2021. Retrieved 2021-03-19.
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