Black opal

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An opal with vivid iridescent colors on a dark background. Black opals were first discovered in 1902 at Lightning Ridge in New South Wales, Australia. Black opals display different color patterns depending on the viewing angle. The colors depend on the crystal size within the stone. When the particles are small, some purple can be seen. Medium sized particles diffract green and larger particles show red.

Synonyms and Related Terms

ópalo negro (Esp.); opala negra (Port.)

Other Properties

Massive with no crystalline structure. Cleavage=none Luster = vitreous to pearly. Fracture = conchoidal. Streak = white

Iridescent. Fluoresce=usually white or pale green, some samples phosphoresce

Mohs Hardness 5.5 - 6.5
Density 1.98-2.25
Refractive Index 1.42-1.47

Hazards and Safety

Chronic inhalation may cause lung damage

Dehydration may cause surface cracking

Additional Information

Mineralogy Database: Opal

Sources Checked for Data in Record

  • Yasukazu Suwa, Gemstones: Quality and Value, Volume 1, Sekai Bunka Publishing Inc., Tokyo, 1999
  • Michael O'Donoghue and Louise Joyner, Identification of Gemstones, Butterworth-Heinemann, Oxford, 2003