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Opal: Brazil and Mexico
Current inventory:  0 gems
 

Chemistry:  SiO₂ + 5-10% nH₂O

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

Classification

Mineral Classification:

Oxides

Strunz 8th Ed. ID:

4/D.01-80

4 : Oxides & Hydroxides
D : Oxides with metal : oxygen = 1:2 (MO2 and related compounds)
01 : Quartz group

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.

Physical Properties

Cleavage:

None (amorphous)

Fracture:

Conchoidal

Tenacity:

Brittle

Moh's Hardness:

5.5 - 6.0

Density:

1.90 - 2.30 (g/cm³)

Radioactivity:

Not Radioactive

Optical Properties

Color:

Colorless, white, yellow, orange, red, yellowish brown, greenish, blue, gray, black, violet.

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.

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 Brazil and Mexico.
 

  
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