tourmaline

n. variety of hard borosilicate mineral with varying colors and compositions (Geology)

The tourmaline mineral group is chemically one of the most complicated groups of silicate minerals. Its composition varies widely because of isomorphous replacement (solid solution), and its general formula can be written as XY3Z6(T6O18)(BO3)3V3W, where: X = Ca, Na, K, vacancy
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Noun
1. a mineral that is a complex borosilicate and hydroxide of aluminum containing iron and magnesium and calcium and lithium and sodium; it is usually black but occurs in transparent colored forms that are used as gemstones
(hypernym) transparent gem
(hyponym) schorl

(n.)
A mineral occurring usually in three-sided or six-sided prisms terminated by rhombohedral or scalenohedral planes. Black tourmaline (schorl) is the most common variety, but there are also other varieties, as the blue (indicolite), red (rubellite), also green, brown, and white. The red and green varieties when transparent are valued as jewels.
  

General Information:
 Chemical Formula:
NaFe+++3Al6(BO3)3Si6O21F
 Composition:
(Molecular Weight = 1,228.77 gm)
Sodium 1.87 % Na
Aluminum 13.17 % Al
Iron 13.63 % Fe
Silicon 13.71 % Si
Boron 5.28 % B 
Oxygen 50.78 % O 
Fluorine 1.55 % F 
 Empirical Formula:
NaFe3+3Al6(BO3)3Si6O21F
 IMA Status:
Approved IMA 1966
Physical Properties:
 Cleavage:
[???] Good
 Color:
bronze, dark brown, or black.
 Density:
3.31
 Diaphaniety:
Translucent to Opaque
 Hardness:
7 - Quartz
 Streak:
yellowish brown
More details...

General Information:
 Chemical Formula:
NaMg3Al6(BO3)3Si6O18(OH)4
 Composition:
(Molecular Weight = 1,135.17 gm)
Sodium 2.03 % Na
Magnesium 6.42 % Mg
Aluminum 14.26 % Al
Silicon 14.84 % Si
Boron 5.71 % B 
Hydrogen 0.36 % H 
Oxygen 56.38 % O 
 Empirical Formula:
NaMg3Al6(BO3)3Si6O18(OH)4
 Environment:
Metasomatically altered magnesian or dolomitic limestones in contact-metamorphic aureoles.
 Locality:
Drava River, Austria.
 Name Origin:
After its locality.
Physical Properties:
 Cleavage:
[???] Indistinct
 Color:
black, green, red, blue, or white.
 Density:
2.98 - 3.2, Average = 3.09
 Diaphaniety:
Transparent to translucent to opaque
 Habits:
Massive - Uniformly indistinguishable crystals forming large masses., Columnar - Forms columns, Divergent - Crystals radiate from a center without producing stellar forms.
 Hardness:
7-7.5
 Luminescence:
Non-fluorescent.
 Luster:
Vitreous - Resinous
 Streak:
colorless
More details...

General Information:
 Chemical Formula:
(Ca,Na)(Fe,Mg,Ti)3(Al,Mg,Fe)6(BO3)3Si6O18(OH)4
 Composition:
(Molecular Weight = 1,224.34 gm)
Sodium 0.47 % Na
Calcium 2.46 % Ca
Magnesium 5.36 % Mg
Titanium 1.17 % Ti
Aluminum 7.93 % Al
Iron 10.95 % Fe
Silicon 13.76 % Si
Boron 5.30 % B 
Hydrogen 0.33 % H 
Oxygen 52.27 % O 
 Empirical Formula:
Ca0.75Na0.25Fe2+2.4Mg2.7Ti0.3Al3.6(BO3)3Si6O18(OH)4
 IMA Status:
Approved IMA
Physical Properties:
 Cleavage:
None
 Color:
brownish black, dark brown, or black.
 Density:
3.207
 Diaphaniety:
Translucent to Opaque
 Hardness:
7 - Quartz
 Luster:
Vitreous - Dull
 Streak:
gray
More details...

General Information:
 Chemical Formula:
[ ]Na<0.5(Fe++,Al)3Al6Si6O18(BO3)3(OH)4
 Composition:
(Molecular Weight = 1,208.15 gm)
Sodium 1.90 % Na
Aluminum 15.07 % Al
Iron 10.40 % Fe
Silicon 13.95 % Si
Boron 5.37 % B 
Hydrogen 0.33 % H 
Oxygen 52.97 % O 
 Empirical Formula:
NaFe3+2.25Al6.75Si6O18(BO3)3(OH)4
 IMA Status:
Approved IMA
Physical Properties:
 Cleavage:
None
 Color:
bluish black.
 Density:
3.17
 Diaphaniety:
Translucent to Opaque
 Hardness:
7 - Quartz
 Luster:
Vitreous (Glassy)
 Streak:
gray white
More details...

General Information:
 Chemical Formula:
Ca(Li,Al)3Al6(BO3)3Si6O18(O,OH,F)4
 Composition:
(Molecular Weight = 1,114.18 gm)
Lithium 1.40 % Li
Calcium 3.60 % Ca
Aluminum 16.35 % Al
Silicon 15.12 % Si
Boron 5.82 % B 
Hydrogen 0.14 % H 
Oxygen 56.72 % O 
Fluorine 0.85 % F 
 Empirical Formula:
CaLi2.25Al6.75BO33Si6O20(OH)1.5F0.5
 IMA Status:
Approved IMA 1977
Physical Properties:
 Cleavage:
None
 Color:
blue, brown, green, pink, or red.
 Density:
3.02
 Diaphaniety:
Transparent to Subtranslucent
 Hardness:
7.5 - Garnet
 Luster:
Vitreous (Glassy)
 Streak:
white
More details...

General Information:
 Chemical Formula:
NaAl3Al6(BO3)3(Si6O18)(O,OH)4
 Composition:
(Molecular Weight = 1,140.18 gm)
Sodium 2.02 % Na
Aluminum 21.30 % Al
Silicon 14.78 % Si
Boron 5.69 % B 
Hydrogen 0.09 % H 
Oxygen 56.13 % O 
 Empirical Formula:
NaAl9(BO3)3Si6O21(OH)
 IMA Status:
Approved IMA
Physical Properties:
 Color:
light pink.
 Density:
3.01
 Diaphaniety:
Transparent
 Hardness:
7 - Quartz
 Luster:
Vitreous (Glassy)
 Streak:
white
More details...

General Information:
 Chemical Formula:
(Na,K)(Fe+++,Fe++)3(Fe,Mg,Al)6(BO3)3Si6O18(OH)4
 Composition:
(Molecular Weight = 1,332.93 gm)
Potassium 0.73 % K 
Sodium 1.29 % Na
Magnesium 3.28 % Mg
Aluminum 1.21 % Al
Iron 27.65 % Fe
Silicon 12.64 % Si
Boron 4.87 % B 
Hydrogen 0.30 % H 
Oxygen 48.01 % O 
 Empirical Formula:
Na0.75K0.25Fe3+2.25Fe2+0.75Fe2+3.6Mg1.8Al0.6(BO3)3(Si6O
 IMA Status:
Approved IMA
Physical Properties:
 Cleavage:
None
 Color:
black.
 Density:
3.26
 Diaphaniety:
Translucent
 Hardness:
7 - Quartz
 Luster:
Resinous
 Streak:
brown
More details...

General Information:
 Chemical Formula:
NaFe++3Al6(BO3)3Si6O18(OH)4
 Composition:
(Molecular Weight = 1,044.39 gm)
Aluminum 15.50 % Al
Iron 16.04 % Fe
Silicon 16.14 % Si
Boron 3.11 % B 
Hydrogen 0.39 % H 
Nitrogen 1.34 % N 
Oxygen 47.49 % O 
 Empirical Formula:
NFe3+3Al6BO33Si6O18(OH)4
 Environment:
Granites, diorites, gabbro pegmatites, greisens, skarns and quartz veins.
 Locality:
Sonnenberg, Bodenmais and Spessart, Germany.
 Name Origin:
Old name of unknown origin.
Physical Properties:
 Cleavage:
[1011] Indistinct
 Color:
black, brownish black, greenish black, or bluish black.
 Density:
3.1 - 3.2, Average = 3.15
 Diaphaniety:
Opaque
 Habits:
Acicular - Occurs as needle-like crystals., Prismatic - Crystals Shaped like Slender Prisms (e.g. tourmaline)., Striated - Parallel lines on crystal surface or cleavage face.
 Hardness:
7.5 - Garnet
 Luminescence:
Piezoelectric.
 Luster:
Vitreous (Glassy)
 Streak:
brown
More details...

General Information:
 Chemical Formula:
(Ca,Na)(Mg,Fe++)3Al5Mg(BO3)3Si6O18(OH,F)4
 Composition:
(Molecular Weight = 970.23 gm)
Sodium 0.59 % Na
Calcium 3.10 % Ca
Magnesium 5.64 % Mg
Aluminum 13.90 % Al
Iron 4.32 % Fe
Silicon 17.37 % Si
Boron 3.34 % B 
Hydrogen 0.31 % H 
Oxygen 49.47 % O 
Fluorine 1.96 % F 
 Empirical Formula:
Ca0.75Na0.25Mg2.25Fe2+0.75Al5(BO3)3Si6O18(OH)3F
 Environment:
Pegmatitic and skarn rocks.
 Locality:
Province Uva, Sri Lanka.
 Name Origin:
Named after its locality.
Physical Properties:
 Cleavage:
[1011] Indistinct
 Color:
yellowish brown, brown, blackish brown, or bluish black.
 Density:
3.1 - 3.2, Average = 3.15
 Diaphaniety:
Translucent to opaque
 Habits:
Striated - Parallel lines on crystal surface or cleavage face., Prismatic - Crystals Shaped like Slender Prisms (e.g. tourmaline).,
 Hardness:
7.5 - Garnet
 Luminescence:
Piezoelectric.
 Luster:
Vitreous - Greasy
 Streak:
light brown
More details...