Opal and natural amorphous silica materials
Natural hydrous amorphous silica gem materials and their body-colour varieties; must be kept separate from synthetic, assembled and imitation opal.
What this family is
Three kinds stay outside: opal that was synthesised, opal that was assembled, and opal that merely imitates. What the family holds is silica in its natural, hydrous, amorphous form: black, white and fire opal as body-colour varieties, crystal opal defined by transparency instead, plus boulder, matrix and hydrophane opal.
Boulder opal is not an assembled stone, yet polymer filling of its voids must be disclosed; hydrophane absorbs dyes, sugar solutions and resins; sugar-acid treatment of matrix opal is very common.
Scope of this family
Natural hydrous amorphous silica gem materials and their body-colour varieties; must be kept separate from synthetic, assembled and imitation opal.
Common confusions
Names in this family that do not by themselves say what the material is, and man-made or assembled products recorded against its materials. Each line says what the item actually is.
Synthetic, assembled or treated counterparts
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| Name | Counterpart of | What it actually is |
|---|---|---|
| Synthetic Opal | Opal | Man-made opal with essentially the same composition, physical properties and structure as natural Opal; the name may be used only when the material has been verified to meet this definition. |
Member entries (16)
Treatments recorded on member entries
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| Treatment | Member entries | Disclosure requirement |
|---|---|---|
| Heated / Heat-treated | Black Opal | Heating is a common treatment, and acceptance varies by material. Whether heated ruby or sapphire must be declared separately depends on which code is followed (see the comparison on this page); unstable colour or foreign residues must be disclosed. |
| Filled / Fracture-filled | Black Opal, Boulder Opal, Common Opal, Coober Pedy Opal, Crystal Opal, Fire Opal, Hydrophane Opal, Lightning Ridge Opal, Matrix Opal, Moss Opal, Opal, Precious Opal, White Opal | Name the filler (resin, oil, polymer, glass or lead glass) and bear in mind that fillings can be unstable and may deteriorate or change colour over time. LMHC Information Sheet #3 treats corundum with glass in two ways: glass in fissures or cavities is still reported on natural corundum as a filling, and only a badly fractured single piece infused throughout, or small fragments bound together with glass, is reported as a manufactured product. |
| Dyed | Black Opal, Boulder Opal, Common Opal, Coober Pedy Opal, Crystal Opal, Fire Opal, Hydrophane Opal, Lightning Ridge Opal, Matrix Opal, Moss Opal, Opal, Precious Opal, White Opal | Must be disclosed. Dye may fade, bleed or dissolve in solvents (alcohol, acetone), and dyed material must not be labelled "natural colour"; dyed jadeite counts as B/C jade and must be conspicuously labelled; dyed agate and chalcedony are extremely common. |
| Coated | Black Opal, Boulder Opal, Common Opal, Coober Pedy Opal, Crystal Opal, Fire Opal, Hydrophane Opal, Lightning Ridge Opal, Matrix Opal, Moss Opal, Opal, Precious Opal, White Opal | Must be disclosed. Coatings may be abraded, flake off or discolour, and coating is not a permanent enhancement; the coating material must be disclosed (e.g. Mystic Topaz is coated topaz), and the treated effect must not be implied to be natural. |
| Impregnated | Black Opal, Opal, White Opal | Must be disclosed. Where the impregnation also brings colour, as in jadeite that has been acid-treated and then impregnated with polymer and colour, or Zachery-treated turquoise, the colouring is part of what has to be declared. |
Care codes on member entries
Member entries cite these CIBJO special-care codes: special-care code b, special-care code c, special-care code d, special-care code e, special-care code f, special-care code j, special-care code k. General gem care gives the full wording of every code.
Where members are recorded
Some member entries record the localities where their materials are found; Recorded localities shows them on a sketch map and lists them by continent.
Names
- 简体中文
- 欧泊与天然非晶质二氧化硅材料
- 繁體中文
- 歐泊與天然非晶質二氧化矽材料
- English
- Opal and natural amorphous silica materials
- 日本語
- オパール・天然非晶質シリカ材料
Authority source
- Authority source
- Review status
- Reviewed against CIBJO, GB/T and IMA boundaries.
Distribution across the other axes
All 16 members share these values:
- Origin class
- Natural materials
- Material domain
- Natural inorganic gem materials
- Mineral chemical class
- Not applicable
- Construction or treatment status
- Natural identity; treatment status unknown