Opal Mineral Data

General Opal Information

Chemical Formula:

SiO2•n(H2O)

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

Empirical Formula:

SiO₂•1.5(H₂O)

Environment:

Sedimentary and secondary from the alteration of high silica igneous extrusive rocks.

IMA Status:

Valid Species (Pre-IMA) Prehistoric

Locality:

World wide occurrences. Link to MinDat.org Location Data.

Name Origin:

From the Old Indian upala - "precious stone."

Name Pronunciation:

Opal

Synonym:

Fire Opal - red

Hyalite - glassy

Hydrophane - porous

Prase - green

Precious opal - opalescent

Opal Image

Images:

Opal

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

Images:

Opal

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

Images:

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

Crystal System:

Amorphous- No Crystals

Physical Properties of Opal

Cleavage:

None

Color:

White, Yellow, Red, Brown, Blue.

Density:

1.9 - 2.3, Average = 2.09

Diaphaneity:

Transparent to translucent to opaque

Fracture:

Conchoidal - Fractures developed in brittle materials characterized by smoothly curving surfaces, (e.g. quartz).

Habit:

Amorphous - No crystalline form or imitative shape.

Habit:

Massive - Uniformly indistinguishable crystals forming large masses.

Habit:

Reniform - "Kidney like" in shape (e.g.. hematite).

Hardness:

5.5-6 - Knife Blade-Orthoclase

Luminescence:

Fluorescent, Short UV=greenish yellow, Long UV=white.

Luster:

Vitreous - Dull

Streak:

white

Optical Properties of Opal

Gladstone-Dale:

CI meas= 0.177 (Poor) - where the CI = (1-KPDmeas/KC)
KPDmeas= 0.2048,KC= 0.2489
Ncalc = 1.47 - 1.57

Optical Data:

Isotropic, n=1.43.

Calculated Properties of Opal

Electron Density:

Bulk Density (Electron Density)=2.17 gm/cc
note: Specific Gravity of Opal =2.10 gm/cc.

Fermion Index:

Fermion Index = 0.01
Boson Index = 0.99

Photoelectric:

PE_Opal= 1.32 barns/electron
U=PE_Opal x rElectron Density= 2.86 barns/cc.

Radioactivity:

GRapi = 0 (Gamma Ray American Petroleum Institute Units)
Opal is Not Radioactive

Opal Classification

Dana Class:

75.02.01.01 (75)Tectosilicate Si Tetrahedral Frameworks

(75.02)SiO2 with H2O and organics

(75.02.01)Dana Group

75.02.01.01 Opal SiO2•n(H2O) None

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

References:

NAME( Duda&Rejl90) PHYS. PROP.(Dana) OPTIC PROP.(Enc. of Minerals,2nd ed.,1990)

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Print or Cut-and-Paste your Opal Specimen Label here :

Opal

SiO2•n(H2O)
Dana No: 75.02.01.01 Strunz No: 04.DA.10
Locality:

Notes:

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