Topaz Mineral Data

Topaz Mineral Data +

General Topaz Information

Chemical Formula:

Al2SiO4(F,OH)2

Composition:

Molecular Weight = 182.25 gm

Aluminum 29.61 % Al 55.95 % Al₂O₃

Silicon 15.41 % Si 32.97 % SiO₂

Hydrogen 0.50 % H 4.45 % H₂O

Oxygen 43.02 % O

Fluorine 11.47 % F 11.47 % F

- % F -4.83 % -O=F₂

______ ______

100.00 % 100.00 % = TOTAL OXIDE

Empirical Formula:

Al₂(SiO₄)F_1.1(OH)_0.9

Environment:

Pegmatites and high temperature quartz veins. Cavities in granites and rhyolites. Deposited by fluorine-rich vapors in rocks of rhyolite composition.

IMA Status:

Valid Species (Pre-IMA) Prehistoric

Locality:

Topasos Island in the Red Sea. Link to MinDat.org Location Data.

Name Origin:

Named after its locality.

Synonym:

Pycnite - yellowish white-

Topaz Image

Images:

Topaz

Comments: Transparent sharp gem topaz crystal set upon a matrix of crystallized white albite and silvery muscovite.
Location: Yunu Village, Shigar, Gilgit division, Pakistan. Scale: 1.6 x 1.8 x 4.2 cm.
© Dan Weinrich

Topaz Crystallography

Axial Ratios:

a:b:c =0.4943:1:0.9545

Cell Dimensions:

a = 4.35, b = 8.8, c = 8.4, Z = 4; V = 321.55 Den(Calc)= 3.76

Crystal System:

Orthorhombic - DipyramidalH-M Symbol (2/m 2/m 2/m) Space Group: Pbnm

$Help on X Ray Diffraction:$ X Ray Diffraction:

By Intensity(I/I_o): 2.937(1), 3.195(0.65), 3.369(0.6),

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Forms: [ 0 1 0] [ 0 2 1] [ 1 1 1] [ 0 1 1] [ 1 1 2] [ 1 2 0] [ 1 1 0] [ 0 0 1]

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Crystal Structure:

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Wunder B , Rubie D C , Ross C R , Medenbach O , Seifert F , Schreyer W , American Mineralogist , 78 (1993) p.285-297, Synthesis, stability, and properties of Al2SiO4(OH)2: A fully hydrated, analogue of topaz

View Additional jPOWD Structure files for Topaz
[1] [3] [4] [5] [6] [7] [8] [9]

Physical Properties of Topaz

Cleavage:

[001] Perfect

Color:

Colorless, Pale blue, Yellow, Yellowish brown, Red.

Density:

3.5 - 3.6, Average = 3.55

Diaphaniety:

Transparent

Fracture:

Brittle - Uneven - Very brittle fracture producing uneven fragments.

Habit:

Crystalline - Coarse - Occurs as well-formed coarse sized crystals.

Habit:

Massive - Granular - Common texture observed in granite and other igneous rock.

Habit:

Prismatic - Crystals Shaped like Slender Prisms (e.g. tourmaline).

Hardness:

8 - Topaz

Luminescence:

Fluorescent, Short UV=golden yellow, Long UV=cream.

Luster:

Vitreous (Glassy)

Streak:

white

Optical Properties of Topaz

Gladstone-Dale:

CI meas= 0.146 (Poor) - where the CI = (1-KPDmeas/KC)
CI calc= 0.193 (Poor) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.1653,KPDmeas= 0.1751,KC= 0.2049

Optical Data:

Biaxial (+), a=1.606-1.629, b=1.609-1.631, g=1.616-1.638, bire=0.0090-0.0100, 2V(Calc)=58-68, 2V(Meas)=48-68. Dispersion noticeable, r > v.

Pleochroism (x):

colorless.

Pleochroism (y):

colorless.

Pleochroism (z):

colorless.

Calculated Properties of Topaz

Electron Density:

r_electron=3.51 gm/cc
note: r_Topaz=3.55 gm/cc.

Fermion Index

Fermion Index = 0.0074
Boson Index = 0.9926

Photoelectric:

PE_Topaz= 1.53 barns/electron
U=PE_Topaz x r_electron= 5.36 barns/cc.

Radioactivity:

GRapi = 0 (Gamma Ray American Petroleum Institute Units)

Topaz is Not Radioactive

Topaz Classification

Dana Class:

52.3.1.1 (52)Nesosilicate Insular SiO4 Groups and O, OH, F, and H2O

(52.3)with cations in [6] coordination only

(52.3.1)Dana Group

52.3.1.1 Topaz Al2SiO4(F,OH)2 Pbnm 2/m 2/m 2/m

52.3.1.2 IMA2000-043a! (Al,Ga)2(Ge,C)O4(OH)2 P nma 2/m 2/m 2/m

Strunz Class:

VIII/B.02-70 VIII - Silicates

VIII/B - Nesosubsilicates, with anions unfamiliar to tetraheders, cations of octahedral and tetrahedral orientation [4/6]

VIII/B.02 - Disthene series

VIII/B.02-10 Sillimanite Al2SiO5=Al[6]Al[4]OSiO4 P nma 2/m 2/m 2/m

VIII/B.02-20 Andalusite Al2SiO5=Al[6]Al[5]OSiO4 Pnnm 2/m 2/m 2/m

VIII/B.02-30 Kanonaite (Mn,Al)AlSiO5 Pnnm 2/m 2/m 2/m

VIII/B.02-40 Kyanite Al2SiO5=Al[6]Al[6]OSiO4 P1 1

VIII/B.02-50 Mullite Al(42x)Si(2-2x)O(10-x)wherex=0.17to0.59 Pbam 2/m 2/m 2/m

VIII/B.02-60 Yoderite Mg2(Al,Fe)6Si4O18(OH)2 P 2₁ 2

VIII/B.02-70 Topaz Al2SiO4(F,OH)2 Pbnm 2/m 2/m 2/m

Other Topaz Information

References:

NAME( Duda&Rejl90) PHYS. PROP.(Enc. of Minerals,2nd ed.,1990) OPTIC PROP.(Heinrich65)

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Topaz

Al2SiO4(F,OH)2
Dana No: 52.3.1.1 Strunz No: VIII/B.02-70
Locality:

Notes: