Tridymite Mineral Data

Tridymite Mineral Data +

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General Tridymite Information

Chemical Formula:

SiO2

Composition:

Molecular Weight = 60.08 gm

Silicon 46.74 % Si 100.00 % SiO₂

Oxygen 53.26 % O

______ ______

100.00 % 100.00 % = TOTAL OXIDE

Empirical Formula:

(SiO₂)

Environment:

Cavities in volcanic rocks.

IMA Status:

Valid Species (Pre-IMA) 1868

Locality:

Occurs world wide. Link to MinDat.org Location Data.

Name Origin:

From the Greek Tridymos - "triplex."

Tridymite Image

Images:

Tridymite

Comments: Clear, pseudohexagonal crystals of tridymite on matrix.
Location: Bellerberg quarry, Laacher See, Rhineland-Palatinate, Germany. Scale: Not Given.
© Lou Perloff / Photo Atlas of Minerals

Tridymite Crystallography

Axial Ratios:

a:b:c =0.5769:1:4.7551

Cell Dimensions:

a = 9.932, b = 17.216, c = 81.864, Z = 330; alpha = 90°, beta = 90°, gamma = 90° V = 13,997.87 Den(Calc)= 2.35

Crystal System:

Triclinic - PedialH-M Symbol (1) Space Group: F1

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

By Intensity(I/I_o): 4.107(1), 4.328(0.9), 3.818(0.5),

Crystal Structure:

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Dollase W A , Baur W H , American Mineralogist , 61 (1976) p.971-978, The superstructure of meteoritic low tridymite solved by computer simulation

View Additional jPOWD Structure files for Tridymite
[1] [2] [3] [4]

Physical Properties of Tridymite

Cleavage:

[0001] Indistinct, [1010] Imperfect

Color:

Colorless, White, Yellowish white, Gray.

Density:

2.28 - 2.33, Average = 2.3

Diaphaniety:

Transparent to translucent

Fracture:

Brittle - Conchoidal - Very brittle fracture producing small, conchoidal fragments.

Habit:

Platy - Sheet forms (e.g. micas).

Habit:

Spherical - Spherical, rounded aggregates.

Hardness:

6.5-7 - Pyrite-Quartz

Luminescence:

Non-fluorescent.

Luster:

Vitreous (Glassy)

Magnetism:

Nonmagnetic

Streak:

white

Optical Properties of Tridymite

Gladstone-Dale:

CI meas= 0.002 (Superior) - where the CI = (1-KPDmeas/KC)
CI calc= 0.021 (Excellent) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2035,KPDmeas= 0.2075,KC= 0.208

Optical Data:

Biaxial (+), a=1.471-1.482, b=1.472-1.483, g=1.474-1.488, bire=0.0030-0.0060, 2V(Calc)=50-72, 2V(Meas)=36-90. Dispersion none.

Pleochroism (x):

colorless.

Pleochroism (y):

colorless.

Pleochroism (z):

colorless.

Calculated Properties of Tridymite

Electron Density:

r_electron=2.30 gm/cc
note: r_Tridymite=2.31 gm/cc.

Fermion Index

Fermion Index = 0.02208
Boson Index = 0.97792

Photoelectric:

PE_Tridymite= 1.80 barns/electron
U=PE_Tridymite x r_electron= 4.14 barns/cc.

Radioactivity:

GRapi = 0 (Gamma Ray American Petroleum Institute Units)

Tridymite is Not Radioactive

Tridymite Classification

Dana Class:

75.1.2.1 (75)Tectosilicate Si Tetrahedral Frameworks

(75.1)SiO2 with [4] coordinated Si

(75.1.2)Dana Group

75.1.2.1 Tridymite SiO2 F1 1

Strunz Class:

IV/D.01-20 IV - Oxides

IV/D - Oxides with metal : oxygen = 1:2 (MO2 and related compounds)

IV/D.01 - Quartz group

IV/D.01-10 Quartz SiO2 P 3₁21,P 3₂21 3 2

IV/D.01-20 Tridymite SiO2 F1 1

IV/D.01-30 Cristobalite SiO2 P 4₁2₁2 4 2 2

IV/D.01-35 Moganite! SiO2 I2/a 2/m

IV/D.01-40 Melanophlogite SiO2·n(C,H,O,S) P 4₁/nbc 4/m 2/m 2/m

IV/D.01-40* Melanophlogite-beta! SiO2·n(C,H,O,S) P m3n 4/m 3 2/m

IV/D.01-50 Coesite SiO2 C 2/c 2/m

IV/D.01-60 Stishovite SiO2 P 4/mnm 4/m 2/m 2/m

IV/D.01-70 Lechatelierite* SiO2 None

IV/D.01-80 Opal SiO2·n(H2O) None

Other Tridymite Information

References:

NAME( Duda&Rejl90) PHYS. PROP.(Larousse des Mineraux,1981) OPTIC PROP.(Larousse des Mineraux,1981)

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Tridymite

SiO2
Dana No: 75.1.2.1 Strunz No: IV/D.01-20
Locality:

Notes: