Black opal

Tiffany necklace
MFA# 2017.1328

Description

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.)

Risks

• Chronic inhalation may cause lung damage
• Dehydration may cause surface cracking

Physical and Chemical 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 g/ml
Refractive Index	1.42-1.47

Resources and Citations

• Mineralogy Database: Opal

• Wikipedia: http://en.wikipedia.org/wiki/Opal (accessed Oct. 12, 2005)

• 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