Mineral phase
IMA name
beta-Tridymite
Secondary names
Tridymite, high-Tridymite
Type
Class
silicate mineral
Compound type
tektosilicate
Chemical composition
Formula
$SiO_2$
Chemical formula
SiO2
Elemental formula
Si O2
Isotope mixture type
terrestrial abundance
  Formula Name Family Number min-max Isotope mole fraction State Relevance
$Si$ Silicon element 1 constituent element main
$O$ Oxygen element 2 constituent element main
Chemical bonds
  Bond Number
$\geq Si-O-$ 4
Oxides
Formula $SiO_{2}$
Mass fraction (%) 100.0

Strunz

Class
oxides - hydroxides - arsenites (04)
Division
metal:oxygen = 1:2 and similar (04.D)
Family
with small cations: Silica family (04.DA)
Code
04.DA.10

Dana

Major class
silicates (VIII)
Class
tectosilicate Si tetrahedral frameworks (75)
Type
SiO2 with [4] coordinated Si (75.01)
Group
-Tridymite- group (75.01.02)
Code
75.01.02.01
Phase name
beta-Tridymite
Phase type
crystalline
Crystal system
hexagonal
Crystal class
dihexagonal-dipyramidal
Crystal class symbol
6/mmm (D6h)
Crystal spacegroup
P6(3)/mmc
Molar mass
60.08 $g/mol$
Density
2.25 $g/cm^3$
State NTP
metastable solid - other solid
Phase transitions
Phase transition type Other phases Temperature - Pressure
solid-solid alpha-Tridymite below 390 K (117°C)
solid-solid beta-Quartz below 597 K (870°C) at 100 kPa, above 0.7 GPa at 1470°C
solid-solid beta-Cristobalite above 1197 K (1470°C)
Phase transitions comments
the stable phase at NTP is alpha-quartz
Refringence type
uniaxial
Pure color
colorless
Color
colorless, white
Diaphaneity
transparent to translucent
Luster
vitreous
Links