OPAL
Opal
Hydrated silica, an amorphous gem material
A hydrated silica gem. Moving flashes of color, known as play-of-color, are a celebrated characteristic of some varieties.
GEM PROFILE
Basic properties
- Mineral or material
- Hydrated silica, an amorphous gem material
- Main chemical composition
- SiO₂·nH₂O
- Crystal & structure
- Amorphous
Not assigned a conventional crystal system. Arrays of microscopic silica spheres produce play-of-color in some opals.
- Typical colors
- White, black, yellow, orange and other bodycolors; some show play-of-color
- Mohs hardness
- 5–6.5
A measure of scratch resistance, distinct from resistance to impact or breakage.
About hardness and durability - Representative sources
Examples of known sources. Determining the origin of an individual stone requires examination and comparison with reference material.
- Common cutting styles
- Cabochons are typical. Some transparent fire opals are faceted.
Explore cutting styles
LOOK A LITTLE CLOSER
What to observe
Not every opal shows play-of-color. Observe bodycolor, the colors and patterns of the flashes, and transparency separately.
TREATMENT & CARE
Treatments & care
Treatments & identification
Dyeing and impregnation may be encountered. Doublets, triplets and synthetic opal also exist.
Everyday care
Avoid drying conditions, high heat, sudden temperature changes and cleaning equipment. Water absorption and assembled layers affect care; avoid soaking unless appropriate care has been confirmed.
Cleaning depends on treatment, inclusions and mounting. If a stone's condition is unknown, ask your jeweler or a gem specialist before cleaning.
READING & REFERENCES
References
Public sources for learning about this gemstone's general properties.
This dictionary provides general educational information. Values are representative and do not identify or grade an individual stone. Locality examples include historical deposits.
Sources checked: October 19, 2026