Constituent
- Name
- Opal
- IMA name
- Opal
- Class
- silicate mineral
- Compound type
- tektosilicate
- Relevance
- main - major
- Arrangement
- in multi-phases
- Mass fraction
- 1.0
- Formula
- $SiO_2 \bullet n(H_2O)$
- Chemical formula
- SiO2(H2O)n
- Elemental formula
- Si (O)2.1-2.9 (H)0.2-1.8
- Isotope mixture type
- terrestrial abundance
- Composition comments
- water content may range from 3 to 21% by weight, but is usually between 6 and 10% (n = 0.2 - 0.35
- Oxides
-
Formula $SiO_{2}$ $H_{2}O$ Mass fraction (%) 92.0 8.0 - Oxides comments
- values for n=0.3, but mostly vary from 3 to 21% for H2O
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
- with H2O and organics (75.02)
- Group
- -Opal- group (75.02.01)
- Code
- 75.02.01.01
- Phase type
- amorphous
- Crystal system
- amorphous
- Polytypes
-
- Opal-CT (Lussatite) (contains cristobalite-tridymite)
- Opal-C (contains cristobalite)
- Opal-AG (amorphous (Amorphous-Gel))
- Opal-AN (Hyalite) (amorphous (Amorphous-Network))
- Molar mass
- 61.8 - 76.2 $g/mol$
- Density
- 1.25 - 2.3 (av. 2.09) $g/cm^3$
- Refringence type
- isotropic
- Refringence sign
- no
- Birefringence
- 0
- Refraction index $n_{\alpha}$
- 1.370 - 1.470 (typ. 1.43)
- Color
- colorless, white, yellow, red, orange, green, brown, black, blue, pink
- Diaphaneity
- transparent to opaque
- Luster
- vitreous