How to clean it
Damp cloth only. Never ultrasonic, never steam, never leave it in a hot car — opal holds up to 21 percent water and crazes if it dries out.
White, black or transparent with spectral flashes
Opal
The birthstone for October.
Properties
Composition
Hydrated silica (SiO₂·nH₂O) — 3 to 21 percent water by weight
Hardness (Mohs)
5.5–6.5
Crystal system
Amorphous
Colour
White, black or transparent with spectral flashes
Mined in
Australia, Ethiopia, Mexico, Brazil
Worth knowing
The play of colour comes from stacked silica spheres diffracting light — the same physics as a butterfly wing, not pigment.
History
Roman writers ranked it among the most valuable of gems; Australia has dominated supply since the 1890s.
Practical
Caring for Opal
How to tell it is real
Doublets and triplets — a thin opal slice glued to a dark backing — are common and much cheaper. Look at the stone edge-on: a doublet shows a flat glue line.
One general rule covers most mistakes: never store stones loose together. Diamond at 10 on the Mohs scale scratches everything else you own, and it does not need much contact to do it.
What that hardness means in practice
Softer than household dust. Better in earrings or a pendant than in a ring, where it takes constant knocks.
Traditional associations
Opal is traditionally linked to imagination, emotional range and creative flow. In chakra systems it is placed at the Crown, Heart, and in elemental correspondence it is assigned to Water.
These are cultural associations recorded across various traditions, not claims about physical effects. The composition and hardness above are measurable; this paragraph is folklore, and worth reading as such.
Questions
What is Opal made of?
Hydrated silica (SiO₂·nH₂O) — 3 to 21 percent water by weight, crystallising in the amorphous system.
Which month is Opal the birthstone for?
October.
Where does Opal come from?
Australia, Ethiopia, Mexico, Brazil.
How do I clean Opal?
Damp cloth only. Never ultrasonic, never steam, never leave it in a hot car — opal holds up to 21 percent water and crazes if it dries out.
How can I tell if Opal is real?
Doublets and triplets — a thin opal slice glued to a dark backing — are common and much cheaper. Look at the stone edge-on: a doublet shows a flat glue line.
Can I wear it every day?
At 5.5–6.5 on the Mohs scale, not in a ring. Keep it to pieces that take fewer knocks.