Taos Rockers
229 A Camino de la Placita, Taos, NM, 87571


Black Opal Cabochon

Black Opal Cabochon


Australia’s national gemstone (Worlds Most Rare)

Category:       Mineraloid

Formula:        (repeating unit) Hydrated silica. SiO2·nH2O

Crystal system: Amorphous[1]

Color:             Colorless, white, yellow, red, orange, green, brown, black, blue, pink

Crystal habit: Irregular veins, in masses, in nodules

Cleavage:      None[1]

Fracture:        Conchoidal to uneven[1]

Mohs scale hardness:         5.5–6[1]

Luster:            Subvitreous to waxy[1]

Streak:            White

Diaphaneity: opaque, translucent, transparent

Specific gravity:        2.15+0.08−0.90[1]

Density:         2.09

Polish luster: Vitreous to resinous[1]

Optical properties:    Single refractive, often anomalous double refractive due to strain[1]

Refractive index:      1.450+0.020−0.080

(Mexican opal may read as low as 1.37, but typically reads 1.42–1.43[1]

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