alpha-Cristobalite | SSHADE

Mineral phase

IMA name: alpha-Cristobalite

Name and identifiers

Secondary names: Cristobalite, low-cristobalite

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 functions and bonds

Chemical bonds

	Bond	Number
	$\geq Si-O-$	4

Oxides composition

Oxides

Formula	$SiO_{2}$
Mass fraction (%)	100.0

Classifications

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.15

Dana

Major class: silicates (VIII)
Class: tectosilicate Si tetrahedral frameworks (75)
Type: SiO2 with [4] coordinated Si (75.01)
Group: Cristobalite group (75.01.01)
Code: 75.01.01.01

Crystallography

Phase name: alpha-Cristobalite
Phase type: crystalline
Crystal system: tetragonal
Crystal class: trapezohedral
Crystal class symbol: 422 (D4)
Crystal spacegroup: P4(1)2(1)2

Physical properties

Molar mass: 60.08 $g/mol$
Density: 2.32 - 2.36 $g/cm^3$

Thermodynamical properties

State NTP

metastable solid - other solid

Phase transitions

Phase transition type	Other phases	Temperature - Pressure
solid-solid	beta-Cristobalite	above 543 K (270°C)

Phase transitions comments

the stable phase at NTP is alpha-quartz

Optical properties

Refringence type: uniaxial
Refringence sign: negative
Birefringence: 0.003
Refraction index $n_o$ (w): 1.487
Refraction index $n_e$ (e): 1.484
Pure color: colorless
Color: colorless, white, blue gray, brown, gray, yellow
Diaphaneity: transparent to translucent
Luster: vitreous

Links and Publications

Links