Judging quality
Value follows body tone, brightness and breadth of color play, with red the rarest. Doublets and triplets are assembled and worth a fraction of solid opal. Ethiopian opal is hydrophane and will temporarily go clear in water.
Mineraloid
Opal
Hydrated silica whose spheres diffract light into shifting play-of-color. Black opal from Lightning Ridge is the most valuable; Ethiopian Welo opal is the great recent discovery.
Care
Contains water and can craze if dried out or heated. Never ultrasonic; avoid extreme dry heat.
History & lore
Roman writers ranked opal second only to emerald; Australia has supplied the majority of the world's supply since the 1890s.
Cultural history, recorded as tradition rather than as medical or scientific claim.
Common questions about Opal
- What is Opal?
- Hydrated silica whose spheres diffract light into shifting play-of-color. Black opal from Lightning Ridge is the most valuable; Ethiopian Welo opal is the great recent discovery.
- How hard is Opal and what is it made of?
- Opal is a Mineraloid-family mineral with the composition SiO2·nH2O. It crystallizes in the amorphous system and rates 5.5-6.5 on the Mohs hardness scale. It occurs in play-of-color, white, black, orange.
- Where does Opal come from?
- Notable localities for Opal include Australia (Lightning Ridge, Coober Pedy), Ethiopia, Mexico, Brazil.
- How do you tell good Opal from filler?
- Value follows body tone, brightness and breadth of color play, with red the rarest. Doublets and triplets are assembled and worth a fraction of solid opal. Ethiopian opal is hydrophane and will temporarily go clear in water.
- How do you care for Opal?
- Contains water and can craze if dried out or heated. Never ultrasonic; avoid extreme dry heat.
See it in person
Photographs only go so far
Both rooms are open six days a week, and there is always someone happy to pull pieces out of the case so you can compare them under the light.