Opal: USA - Idaho, Nevada, Oregon and other US locations
Current inventory:  3 gems
 

  
Opalus was the ancient Latin name probably derived from the Sanskrit word upala, meaning precious stone. The Greek word opallios literally means "to see a change of color."

Prehistoric Discovery;   IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

SiO₂ + 5-10% nH₂O

Silicon Dioxide + 5-10% H₂O

Molecular Weight:

87.11 gm

Composition:

Silicon

32.24 %

Si

68.98 %

SiO₂

Hydrogen

3.47 %

H

31.02 %

H₂O

Oxygen

64.29 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Oxides

Strunz 8th Ed. ID:

4/D.01-80

Nickel-Strunz 10th Ed. ID:

4.DA.10

4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
D : Metal: Oxygen = 1:2 and similar
A : With small cations: Silica family

Related to:

n/a

Varieties:

None

Synonyms:

Idaho Opal, Nevada Opal, Oregon Opal, Virgin Valley Opal, and other specific location names

Crystal Data

Crystallography:

Amorphous  (no crystalline forms)

Crystal Habit:

Amorphous - (no crystalline forms) Habits include Massive; Concretions; Botryoidal; Stalactitic; Reniform - "kidney like" in shape (e.g. Hematite); cavity fillings (e.g. in fractures and geodes); replacement of other minerals or wood.

Twinning:

None

Physical Properties

Cleavage:

None (amorphous)

Fracture:

Irregular/Uneven, Splintery, Conchoidal

Tenacity:

Brittle

Moh's Hardness:

5.5 - 6.0

Density:

1.90 - 2.30 (g/cm³)

Luminescence:

Fluorescent; greenish yellow under SW UV, white under LW UV

Radioactivity:

Not Radioactive

Optical Properties

Color:

Colorless, white, yellow, orange, red, yellowish brown, greenish, blue, gray, black, violet; rare specimens display a play of color

Transparency:

Transparent to Translucent to Opaque

Luster:

Vitreous, Waxy, Pearly, Dull

Refractive Index:

1.43 Isotropic

Birefringence:

0.00 (Isotropic)

Dispersion:

Weak

Pleochroism:

Distinct; red, orange, yellow, green, blue

Occurances

Geological Setting:

Sedimentary and secondary from the alteration of high silica igneous extrusive rocks. Altering volcanic tuffs, basalts.

Common Associations:

n/a

Common Impurities:

None

Type Locality:

n/a

Year Discovered:

Prehistoric discovery

View mineral photos:

Opal Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

This page contains Opal gems from the USA; Idaho, Nevada, Oregon and other locations. For more general information on Opals and Opals from other locations around the world, please visit our main Opal page.
 

  
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