Mineralogy Database

Opal Mineral Data

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General Opal Information

Help on Chemical  Formula: Chemical Formula: SiO2•n(H2O)
Help on Composition: Composition: Molecular Weight = 87.11 gm
   Silicon   32.24 %  Si   68.98 % SiO2
   Hydrogen   3.47 %  H    31.02 % H2O
   Oxygen    64.29 %  O
            ______        ______ 
            100.00 %      100.00 % = TOTAL OXIDE
Help on Empirical Formula: Empirical Formula: SiO2•1.5(H2O)
Help on Environment: Environment: Sedimentary and secondary from the alteration of high silica igneous extrusive rocks.
Help on IMA Status: IMA Status: Valid Species (Pre-IMA) Prehistoric
Help on Locality: Locality: World wide occurrences. Link to MinDat.org Location Data.
Help on Name Origin: Name Origin: From the Old Indian upala - "precious stone."
Help on Name Pronunciation: Name Pronunciation: Opal Say OPAL
Help on Synonym: Synonym: Fire Opal - red
  Hyalite - glassy
  Hydrophane - porous
  Prase - green
  Precious opal - opalescent

Opal Image

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Comments: Colorful white opal on a sandstone matrix.
Location: Queensland, Australia. Scale: 9 x 6 x 3 cm.
© Isaias Casanova / IC Minerals

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Comments: Section of fossilized tree limb that is now completely replaced by black opal.
Location: Virgin Valley District, Humboldt Co., Nevada, USA. Scale: 20x13x11 mm.
© John Betts - Fine Minerals

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  Todorokite   Opal

Comments: Dendritic todorokite in white opal.
Location: Brosso Mine, Ivrea, Torino, Piemonte, Italy. Scale: See Photo.
© Jeff Weissman / Photographic Guide to Mineral Species

Opal Crystallography

Help on Crystal System: Crystal System: Amorphous- No Crystals

Physical Properties of Opal

Help on Cleavage: Cleavage: None
Help on Color: Color: White, Yellow, Red, Brown, Blue.
Help on Density: Density: 1.9 - 2.3, Average = 2.09
Help on Diaphaneity: Diaphaneity: Transparent to translucent to opaque
Help on Fracture: Fracture: Conchoidal - Fractures developed in brittle materials characterized by smoothly curving surfaces, (e.g. quartz).
Help on Habit: Habit: Amorphous - No crystalline form or imitative shape.
Help on Habit: Habit: Massive - Uniformly indistinguishable crystals forming large masses.
Help on Habit: Habit: Reniform - "Kidney like" in shape (e.g.. hematite).
Help on Hardness: Hardness: 5.5-6 - Knife Blade-Orthoclase
Help on Luminescence: Luminescence: Fluorescent, Short UV=greenish yellow, Long UV=white.
Help on Luster: Luster: Vitreous - Dull
Help on Streak: Streak: white

Optical Properties of Opal

Help on Gladstone-Dale: Gladstone-Dale: CI meas= 0.177 (Poor) - where the CI = (1-KPDmeas/KC)
KPDmeas= 0.2048,KC= 0.2489
Ncalc = 1.47 - 1.57
Help on Optical Data: Optical Data: Isotropic, n=1.43.

Calculated Properties of Opal

Help on Electron Density: Electron Density: Bulk Density (Electron Density)=2.17 gm/cc
note: Specific Gravity of Opal =2.10 gm/cc.
Help on Fermion Index: Fermion Index: Fermion Index = 0.01
Boson Index = 0.99
Help on Photoelectric: Photoelectric: PEOpal = 1.32 barns/electron
U=PEOpal x rElectron Density= 2.86 barns/cc.
Help on Radioactivity: Radioactivity: GRapi = 0 (Gamma Ray American Petroleum Institute Units)
Opal is Not Radioactive

Opal Classification

Help on  Dana Class: Dana Class: (75)Tectosilicate Si Tetrahedral Frameworks
  (75.02)SiO2 with H2O and organics
  (75.02.01)Dana Group Opal SiO2•n(H2O) None
Help on  Strunz Class: Strunz Class: 04.DA.10 04 - OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodate
  04.D - Metal:Oxygen = 1:2 and similar
  04.DA -With small cations
04.DA.10 Opal SiO2•n(H2O) None
04.DA.10 Tridymite SiO2 F1 1

Other Opal Information

Help on References: References: NAME( Duda&Rejl90) PHYS. PROP.(Dana) OPTIC PROP.(Enc. of Minerals,2nd ed.,1990)
Help on See Also: See Also: Links to other databases for Opal :
1 - Alkali-Nuts(English)
2 - Am. Min. Crystal Structure Database
3 - Amethyst Galleries' Mineral Gallery
4 - Athena
5 - CalTech Mineral Spectroscopy
6 - GeoScienceWorld
7 - Glendale Community College
8 - Google Images
9 - Google Scholar
10 - MinDAT
11 - Mineral and Gemstone Kingdom
12 - Mineralienatlas (Deutsch)
13 - Online Mineral Museum
14 - Philatelic Mineralogy
15 - QUT Mineral Atlas
16 - Ruff.Info
17 - Scandinavian mineral gallery
18 - Tradeshop.com - The Rainbow of Gems
19 - University of Texas at Austin
20 - theimage

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Dana No: Strunz No: 04.DA.10





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