On this page
UnderstandWhat it is, what people ask, how far this page goes
Natural inorganic gem materials · Mineral / gemstone variety · Natural identity; treatment status unknown
Moss Opal
Common Opal containing green or black moss-like dendritic inclusions; it is not moss agate, and the identity of the inclusions must be tested. This page compares how the major standards and institutions name it, what must be disclosed when selling it, whether it can be worn every day, how it is treated and identified, and which source each conclusion comes from.
Price, rarity and origin are outside the scope of this wiki.
What this page can answer
This page covers
- How Moss Opal forms and what gives its colourFormation setting, process and timescale; where its colour and optical effects come from, each finding graded and sourced
- How to identify Moss OpalIdentification points from the research literature; how far lab testing can go
- Treatments and enhancements of Moss OpalThe enhancements and treatments the GB/T and JJA/AGL tables list
- Caring for and wearing Moss OpalCleaning, heat, chemicals and light, as the cited sources give them
- Hardness, density and refractive index of Moss OpalEach value with its source and check date
- Moss Opal in English, Chinese and Japanese; national standard namesNames in four languages, the GB/T standard name and the suggested listing name; and: Has any of GIA, FTC, CIBJO or Gem-A put a name for it on record here?
- Listing and disclosing Moss OpalThe listing name to use; what must be disclosed before sale
- Standard clauses that define Moss OpalWhich clause defines it, each cross-checked
What we cannot conclude
- Whether one particular bead is natural, treated or synthetic — only a laboratory report can settle that.
- Geographic origin, unless an origin report accompanies the item.
- Price, rarity or investment value: this wiki covers naming and disclosure only.
Material research: formation, causes and history
What authoritative sources say about how this material forms, what causes its colour and optical effects, where its name comes from and how people have used it. Each statement carries an evidence grade and its sources; it describes the material in general, not any specific piece.
How it forms
Moss opal refers to common opal containing moss-like (dendritic) green or black inclusions. The cited authoritative sources do not give a formal definition of the name 'moss opal', so only mechanistically related evidence can be cited: opal colors are typically caused by minute mineral inclusions colored by transition-metal ions that absorb part of the visible spectrum, with nickel producing green (chrysopal); opal can host rootlet fossils, opaque black octahedra and pyrite cubes; and opal mineralization in host rock can be extremely irregular, occurring as clusters or dendritic nests, veinlets or veins, breccia 'cement' and impregnations. These observations provide mechanism context for a dendritic/moss-like appearance, but the specific material called moss opal must still be identified case by case.
Scope: Used to describe common opal containing dendritic (moss-like) inclusions; because "moss opal" lacks an authoritative definition, its name definition is grade C, and the specific inclusion minerals and colour origin require piece-by-piece identification.
Sources G&G Fall 2013 · G&G Winter 2023
Where it forms
Opal-mineralization setting in host rock: opal occurs very irregularly as clusters or dendritic nests, veinlets or veins, and impregnations.
Sources G&G Winter 2023
How it forms, step by step
Silica-bearing fluids precipitate to form (common) opal within host rock.
Sources G&G Fall 2013
Minute mineral inclusions such as rootlet fossils, opaque black octahedra and pyrite cubes can be trapped in the opal, and such inclusions may take dendritic forms.
Sources G&G Fall 2013
Transition-metal ions in the inclusions absorb part of visible light, giving the opal the corresponding color (e.g. nickel for green).
Sources G&G Fall 2013
Common opal with a moss-like/dendritic appearance is sold as moss opal, but the name lacks an authoritative definition and must be verified case by case.
Sources G&G Fall 2013
Link to appearance
Green or black moss-like/dendritic inclusions on a common-opal (no play-of-color) background; the green can result from transition-metal ions such as nickel, and the inclusion forms relate to minute minerals or rootlet fossils trapped in the opal.
Sources G&G Fall 2013
Timescale
The cited sources give no numeric age or absolute timescale for the formation of moss opal or its inclusions.
Sources G&G Fall 2013
Related base materials
- Opal (common opal): variety-of | Moss opal is common opal containing dendritic (moss-like) inclusions
Supporting findings
Typical inclusions in opal can include rootlet fossils, opaque black octahedra, or pyrite cubes.
Evidence grade AScope: The inclusion list concerns inclusions typical of Ethiopian opal.
Sources G&G Fall 2013
Opal mineralization in host rock is extremely irregular, occurring as clusters or dendritic nests, veinlets or veins.
Evidence grade AScope: This observation comes from a Slovak locality field report; it describes mineralization habit, not moss-like inclusions inside a gem opal.
Sources G&G Winter 2023
Recorded localities
Authoritative sources list the localities below; the list is not exhaustive.
Europe
- Agua Amarga, Níjar, Almería, Spain
Sources Mindat: Opal
Oceania
- Grants Patch, Western Australia, Australia
Sources Mindat: Opal
These are localities recorded by authoritative sources, not an origin finding for any individual piece. The CIBJO Gemstone Book (2022, §4.2.3) says a place of origin names where a gem was mined or harvested, is a matter of opinion, does not imply a level of quality, and that cutting, processing or exporting centres must not be used to imply origin. See how far testing can go on this page, the origin determination guide and the overview of recorded localities.
Causes of colour and optical effects
Opal colors are typically caused by minute mineral inclusions colored by transition-metal ions that absorb part of the visible spectrum, with nickel producing green (chrysopal).
Evidence grade AScope: This color-cause statement concerns opal bodycolor in general, not moss opal specifically.
Sources G&G Fall 2013
Moss opal is a common opal and normally shows no play-of-color; its milky, hazy look comes from diffuse scattering of light by nanoscale silica spheres that are randomly arranged and varied in size (opalescence). Where a piece does flash colours, those flashes must arise from diffraction by an ordered sphere array, as in precious opal.
Evidence grade AScope: The mechanism follows the scattering principle of common opal; 'moss opal' lacks an authoritative definition and its material is common opal, so the claim does not assert play-of-color in any particular stone, nor does it establish locality, natural origin, or treatment.
The 'moss' appearance of moss opal comes from dendritic (moss-like) inclusions within it, such as rootlet fossils, opaque black octahedra, or pyrite cubes; these are inclusions rather than the diffracting structure that would give play-of-color.
Evidence grade AScope: The inclusion list reflects typical contents reported in opal from one source area; the inclusion species and colour cause of a given moss opal require case-by-case identification, and the claim does not establish locality, natural origin, or treatment.
Sources G&G Fall 2013
How it is identified
The dendritic inclusions in moss opal are not proof of its material, and appearance does not establish naturalness or treatment state. Deciding whether a specimen is natural, laboratory-made or imitation/composite material requires laboratory measurement of gemological properties and composition. The conclusion should be issued by a qualified gem laboratory.
Evidence grade AScope: Applies where natural, synthetic and imitation opal must be distinguished; no self-administered criteria are given.
Other research findings
'Moss opal' has no authoritative definition in the cited sources and is a variety/commercial descriptor; the material is common opal, and the inclusion species and color cause behind the moss-like look must be assessed case by case.
Evidence grade CScope: Defines the nature of the name, graded C; it does not assert that any particular material is moss opal.
Sources G&G Fall 2013
Limits of this research
- Research status: Formation, occurrence or other material-specific findings found in authoritative sources
- 'Moss opal' lacks an authoritative definition; the identification here is graded C.
- The cited mechanism evidence (color cause, typical inclusions) concerns opal in general or Ethiopian opal, not moss opal specifically.
- The dendritic-nest description concerns mineralization habit in host rock, not moss-like inclusions inside a gem.
- The cited sources give no numeric age or absolute timescale.
Methodology
- Origin determination and its limits
- Quality grading and value factors
- How gemmology became a technical discipline
Evidence grades
- A
- Standards bodies, government geological surveys, peer-reviewed research and museum records
- B
- Institutional educational material
- C
- Specialist databases or cautious readings
A statement is never graded above its strongest source.
This section is LumaLark's own factual restatement of public authoritative sources, credited item by item; it contains no verbatim excerpts, images or third-party logos.
DecideListing name, disclosure, care and treatments
- Suggested listing name
- Moss Opal
IMA Mineral List 2026-07 “Opal” · CIBJO Gemmological Laboratories Book 2024 §7.2.1.162 “Opal”
Construction or treatment status
Natural identity; treatment status unknown
Treatments recorded for this material: Filled / Fracture-filled (via parent material), Dyed (via parent material), Coated (via parent material)
Related:Disclosure and cautions
This page cannot answer
Natural? · Origin · Price
A lab report settles these; this wiki covers naming and disclosure.
Related:What this page can answer
Answer at a glance
Moss Opal is Common opal with dendritic green or black moss-like inclusions; use "Moss Opal" for listings, and disclose any known treatments.
Evidence
- CIBJO · 7.2.1.162
What this means for you
Before buying, check the recommended listing name "Moss Opal" and any disclosed treatments on this page, and ask the seller for a grading report if in doubt.
Known uncertainty
- Last reviewed
- 2026-09-01
Care and wear
Normal care for every gemstone (CIBJO Gemstone Book §6.1), in brief:
- Handle it gently.
- Store pieces apart when not worn, so they cannot scratch each other.
- Clean with warm soapy water and a soft brush.
- Use ultrasonic cleaners only with caution.
The §6.1 wording and the full list of §6.2 special-care letters cited on this page are on the general gem care page.
The item-by-item care advice that the GIA Care and Cleaning Guide gives for the whole class, and so for Moss Opal, is set out in full under care on the Opal entry.
Care
Each row's “Source & check” expands to the full source; the date beside it is the fact check date.
Treatments and identification leads
One row per treatment, with three standards side by side: how often it occurs and how stable it is (CIBJO), its category in GB/T 16552—2017 Table B.1 (this site's paraphrase) and how the JJA/AGL 2025 table lists it. Each CIBJO value links to its entry under “Testing and market”, where the wording and source are given in full.
This table scrolls sideways on narrow screens.
| Treatment | Market frequency (CIBJO) | Stability (CIBJO) | GB/T 16552 category | JJA/AGL listing | Identification leads |
|---|---|---|---|---|---|
| Filling | — | — | Graded — see §5.4.1, Table 1 | — | — |
| Dyeing | — | — | Treatment | — | — |
| Coating | — | — | Treatment | — | — |
“—” means the cited source gives no value for that item, not “none”. Source: GB/T 16552—2017 Table B.1 (row for Opal)
Whether a treatment has to show in the name differs between the two rule sets (this site’s paraphrase):
- GB/T 16552—2017: a method classed as treatment has to be stated in the name itself — the method put before the name, or added in brackets after it; a method classed as optimization does not need to appear in the name, though one marked “Optimization (annotation required)” still has to be noted in the quality documents. Source: §5.4.2.1 a), b); §5.4.2.2 a)
- CIBJO Gemstone Book 2022: no longer splits treatments into ones that need specific disclosure and ones that need only general disclosure: every treatment is to be disclosed, and the seller tells the buyer which treatment was used and what special care it calls for. Source: §4.2.5 Note 2, §4.2.5.1, pp.14–15
What this table covers
What this page can give
- Registered treatments, their stability and how often they occur (see the table above)
- Identification leads for each treatment, for use when sending a stone for testing
VerifyNames, standards, technical facts, clauses and sources
Names
Recommended listing nameThe suggested listing name for Moss Opal is Moss Opal. Names in four languagesNames are given in Simplified Chinese, Traditional Chinese, English (Moss Opal) and Japanese; the Japanese name shown is the entry's own, and the GSJ (Japan) wording for this name is not yet verified by this site. Chinese standard nameThe GB/T naming counterpart is opal, see GB/T 16552—2017 Table A.2, while the name Moss Opal itself is not listed in the standard. Trade and mineralogical namesThe mineralogical name describes common opal with dendritic green or black moss-like inclusions. Institution usageOn authority wording, GIA, CIBJO and Gem-A are all unchecked, and the FTC text on file has no wording for this name (checked); bodies without a recorded wording show the entry's own English name, which does not represent their position.
- GSJ (Japan) formal name
- モスオパール (not yet checked for this body — the entry's own Japanese name is shown)
- GB/T naming counterpart (this name is not in the standard)
- 欧泊 (GB/T 16552—2017 Table A.2)
- Mineralogical name
- Common opal with dendritic green or black moss-like inclusions
Four-language names
- 简体中文
- 苔藓欧泊
- 繁體中文
- 苔蘚歐泊
- English
- Moss Opal
- 日本語
- モスオパール
See also: Misleading and prohibited trade names · Supplementary name index
Classification
- Origin
- Natural materials
- Material domain
- Natural inorganic gem materials
- Browsing family
- Opal and natural amorphous silica materials
- Identity tier
- Mineral / gemstone variety
- Mineral chemical class
- Not applicable
- Construction or treatment status
- Natural identity; treatment status unknown
Treatments listed by standards
Moss Opal is not registered under its own name in GB/T 16552—2017 Annex B, Table B.1, so this site applies the opal row of Table B.1 to Moss Opal: the treatments listed in the opal row include filling, which is described separately by grades; dyeing is classed as treatment; and coating is classed as treatment. The full content including the effect column is on the Opal entry, and what Table B.1 notes and how the filling grades are defined are explained on the Gem treatments page.
GB/T 16552-2017, Annex B, Table B.1
Under the “Opal” row of Table B.1: Filling Graded — see §5.4.1, Table 1; Dyeing Treatment; Coating Treatment. The full row, with the effect column, is on the Opal page.
What Table B.1 is, and how the “see 5.4.1” grades are defined: see the GB/T 16552: optimization vs treatment page.
What it is and how it's identified
The Mohs hardness of Moss Opal is recorded as 5–6.5; this site notes that the cited clause covers the whole opal species, of which Moss Opal is only one variety. Recorded for opal (the whole class): structure (overall) amorphous; cleavage none; density 1.25–2.23 g/cm³, from the clause value 2.15 with tolerance +0.08/−0.90, the range derived from the tolerance; refractive index 1.37–1.47, from the clause value 1.450 with tolerance +0.020/−0.080, the range derived from the tolerance, and this site notes that the clause has finer ranges and the overall value is recorded; birefringence none; optic character isotropic, with anomalous extinction often seen in fire opal; pleochroism none when untreated; play-of-colour may be seen, and chatoyancy may be seen but is rare; lustre (as a quality factor) vitreous to resinous when untreated. Chemical composition, fluorescence, UV-visible spectrum, infrared spectrum and magnification are recorded for opal (the whole class); see the Opal entry.
Registered material facts
Each row carries its own source and check date and can be cited on its own; “—” means the cited source gives no value, not “none”.
Chemical composition, luminescence, UV-visible spectrum, infrared spectrum, magnification: these whole-class features are given in the cited clause for opal (whole class), so they are not repeated on the Moss Opal page; see the material facts on the Opal entry.
Items below that name the class they cover give the cited clause’s value for that whole class, not a measurement of Moss Opal (how to read class-level values).
Structure
Moss Opal — structure (overall): amorphous (not crystalline)
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- opal (whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.2.3 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Durability
Moss Opal — Mohs hardness: 5–6.5
GIA Opal
Reference points on this site: Talc 1–3, Fluorite 4, Apatite 5–5.5, Orthoclase 6–6.5, Topaz 8, Diamond 10 (Source: GB/T 16553—2017); Gypsum 1.5–2, Calcite 3, Quartz 7 (Source: Handbook of Mineralogy); Corundum 9 (Source: GIA Gem Encyclopedia (care guide))
- Qualification
The clause we cite covers the whole species. This entry is only one variety of it.
Source & check 2026-09-20
- Source
- GIA Gem Encyclopedia — Opal (Gemological Institute of America): Section “FACTS”, “Mohs Hardness” (locator checked 2026-09-28)
- Fact checked on
- 2026-09-20
Moss Opal — cleavage: none
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- opal (whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.2.3 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Moss Opal — stability: chips and cracks easily; porous, so keep it away from coloured liquids; will craze if it loses water, so keep it away from heat and dry air; avoid sudden temperature changes; no ultrasonic cleaning.
CIBJO Gemstone Book 2022
CIBJO Gemstone Book §6.2:special-care code b, special-care code c, special-care code d, special-care code e, special-care code j
- Treatment state
- untreated
Source & check 2026-09-21
- Source
- Fact checked on
- 2026-09-21
Physical properties
Moss Opal — density: 1.25–2.23 g/cm³
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- opal (whole class)
- Qualification
The clause we cite gives 2.15, with a stated tolerance of +0.08 / -0.90. The range shown here is worked out from that.
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.2.3 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Optical
Moss Opal — optic character: isotropic; fire opal commonly shows anomalous extinction.
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- opal (whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.2.3 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Moss Opal — refractive index: 1.37–1.47
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- opal (whole class)
- Qualification
The clause we cite gives 1.450, with a stated tolerance of +0.020 / -0.080. The range shown here is worked out from that.
- General note
- the clause has finer ranges
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.2.3 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Moss Opal — birefringence: none
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- opal (whole class)
Source & check 2026-09-21
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.2.3 (locator checked 2026-09-21)
- Fact checked on
- 2026-09-21
Moss Opal — pleochroism: none
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
- What this covers
- opal (whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.2.3 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Moss Opal — optical effect (play of colour): seen
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- opal (whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.2.3 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Moss Opal — optical effect (chatoyancy): seen; rare
GB/T 16553—2017
- Does this standard apply
- applies to this entry
- What this covers
- opal (whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.2.3 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
- CIBJO definitions
- play of colour, chatoyancy
Quality factors
Moss Opal — quality factor (lustre): vitreous to resinous
GB/T 16553—2017
- Treatment state
- untreated
- Does this standard apply
- applies to this entry
- What this covers
- opal (whole class)
Source & check 2026-09-26
- Source
- GB/T 16553—2017 Gems — Testing (GB/T): §5.2.3 (locator checked 2026-09-26)
- Fact checked on
- 2026-09-26
Each row's “Source & check” expands to the full source; the date beside it is the fact check date.
This material (RI / SG midpoints): 1.42 / 1.74; Closest values: 1Synthetic Opal 1.45 / 2.08, 2Mammoth Ivory 1.53 / 1.75, 3Ivory 1.535 / 1.85, 4Hackmanite 1.483 / 2.27, 5Chrysocolla 1.516 / 2.2
Show the full chart (330 registered materials)
Outside the full chart's range, drawn as triangles at the edge (RI / SG midpoints): Hematite 3.045/5.12, Synthetic Rutile 2.76/4.26, Rutile 2.753/4.23, Synthetic Moissanite 2.67/3.22
Testing and market
The CIBJO laboratory protocol covers Moss Opal under “Opal” (§6.1.56): see identification on the Opal entry; the required tests are listed on the CIBJO laboratory protocol table for Opal.
How far testing can go
Each row's “Source & check” expands to the full source; the date beside it is the fact check date.
Clause-level definitions
Moss Opal is registered in the clause-level definitions under the corresponding entry name Moss Opal, on the basis of GB/T 16552-2017 Annex A. That clause describes moss opal as common opal containing green or black moss-like dendritic inclusions, that is, common opal with such moss-like inclusions. Cross-check result: listed directly in GB/T; not found under a standalone heading of the same name in CIBJO.
This table scrolls sideways on narrow screens.
| Term | Clause | Definition | Cross-check |
|---|---|---|---|
| Moss Opal | GB/T 16552-2017 Annex A | Common opal with dendritic green or black moss-like inclusions | Listed directly by GB/T; CIBJO carries no standalone entry under the same name. |
Evidence and sources
Authority basis and clause sources
Sources
- CIBJO – The World Jewellery Confederation. Gemmological Laboratories Book (Blue Book), Gemmological Commission 2024-1.
- CIBJO – The World Jewellery Confederation. The Gemstone Book (Blue Book), 2022.
- SAMR / SAC (China). GB/T 16552—2017 Gems — Nomenclature.
- RRUFF Project, in partnership with the IMA – International Mineralogical Association. IMA Mineral List.
- Geological Survey of Japan, AIST (Japan). Museum mineral specimens, browse by classification.
Further reading
Related entries and topic cluster
Parent entry and related pages on this site. Rows marked “Planned” are suggested new content and have no link yet.
Related-entry tree for Opal on this site: 17 entries listed by this site's parent-entry links; synthetic, treated and similar entries carry their recorded state after the name; this page (Moss Opal) is marked.
This table scrolls sideways on narrow screens.
| Page | Content | Status |
|---|---|---|
| Browsing family | Opal and natural amorphous silica materials | Live |
| Treatments recorded for this material | Filled / Fracture-filled (via parent material), Dyed (via parent material), Coated (via parent material) | Live |
| Related articles | To be added (placeholder) | Planned |
Who maintains this page
The material facts in the Moss Opal entry are maintained by the LumaLark wiki and matched one by one to the standard clauses or institutional sources they cite: every fact carries its source (with a clause or page locator) and a check date, so it can be traced back to the original; clause-level definitions also carry a cross-check result. The entry exists so that buyers and sellers can check naming, disclosure and material facts item by item.