Both are diamonds. They differ in origin or treatment history, not in material identity.
Identity First, Origin Second
For an unknown colorless stone, the professional sequence is not:
“Is it natural or synthetic?”
The first question is:
“Is it even diamond?”
Only after diamond material identity has been confirmed does it make sense to ask whether the crystal is natural or synthetic. Treatment, quality, provenance, and value follow after that.
This hierarchy prevents one of the most common logical errors in the modern market: automatically interpreting every unusual result as a synthetic diamond, even though the sample may be moissanite, CZ, another simulant, or a complex material.
Nomenclature
ISO 18323:2015 governs permitted descriptors for diamonds, treated diamonds, synthetic diamonds, composites, and imitations. The standard was reconfirmed in 2026 and remains current.
The CIBJO Diamond Blue Book 2026-1 likewise classifies the following separately:
These documents are not identical to the law of every country, but they provide an important professional framework.
At its September 2026 Congress, CIBJO adopted the rule that only the term synthetic be used for industrially produced diamonds (Diamond Blue Book 2026-1); national regulations continue to take precedence where they apply. In the United States, the FTC Jewelry Guides, 16 CFR Part 23, also permit the qualifiers laboratory-grown and laboratory-created (jurisdiction: US).
“Synthetic” Must Have a Subject
The term synthetic does not automatically mean “synthetic diamond.”
Synthetic moissanite is laboratory-produced silicon carbide. Synthetic sapphire is corundum. Synthetic rutile is titanium dioxide.
Each of these materials may imitate diamond, but none becomes diamond as a result.
The material must therefore be identified by its full name.
An Appearance Clue Is Not Identification
Simulants are successful precisely because they can look like diamond.
The key word is combination. One property is often insufficient.
The Scratch Test Should Be Abandoned
Mohs hardness is important for understanding materials, but deliberately scratching an unknown stone or another object is a poor identification procedure.
The test may damage:
the stone being examined;
the setting;
another material;
a surface treatment.
Professional gemology favors nondestructive methods.
Thermal Testers and the Moissanite Problem
Classic thermal diamond testers became important because diamond conducts heat very well, while many older simulants do not.
Synthetic moissanite changed that problem. Its thermal behavior can be sufficiently similar to diamond for some thermal-only devices to produce a diamond-like result.
It follows that:
“diamond” on a thermal tester is not proof of natural diamond origin and, depending on the device, is not necessarily final confirmation of diamond material identity either.
Modern combination testers may use additional electrical or other properties, but their validity always depends on the specific model, sample, and manner of use.
Screening and Identification
Screening quickly separates samples compatible with a particular category from those requiring further analysis.
A result of refer or further testing required is therefore not a diagnosis. It means that the screening procedure did not resolve the item within its validated scope.
This is especially important for melee, mounted jewelry, and heterogeneous groups of stones.
The result of a method developed for loose stones should therefore not be applied uncritically to a mounted stone.
Composites and Hybrids Are Not Simple Simulants
Some objects consist of several materials or layers. In that case, the question “what stone is this?” may be too simple.
It is necessary to describe:
which components are present;
their material nature;
how they are joined or grown;
which part produces the dominant optical effect.
This applies to assembled stones, surface-coated simulants, and natural/CVD hybrid diamonds.
The CIBJO Diamond Blue Book 2026-1 (clause 4.3.3) requires a composite stone to be described by the word doublet (two parts), triplet (three parts), or composite (more than three parts), immediately next to the correct names of the components. The components are named from the upper part downwards and separated by a slash (/); if all parts, excluding the bonding agent, are the same material, that material is named only once. The word is given the same emphasis as the component names, without abbreviations and without an asterisk pointing to a footnote. CIBJO allows a composite stone in which all parts are diamond to be called a composite diamond.
A Simulant Is Not Fraud
Moissanite, CZ, and other simulants are legitimate products when described correctly.
Professional terminology should therefore avoid the expression “fake diamond” as a general category. It is more precise to identify the material by its actual name.
Decision Workflow
For an unknown diamond-like stone:
document the item and its condition;
distinguish the loose, mounted, and melee context;
perform a visual and microscopic examination;
collect nondestructive physical properties;
use a thermal or combination tester only within its validated scope;
exclude or confirm moissanite, CZ, and other simulants;
confirm material identity;
only if the material is diamond, proceed to natural/synthetic origin;
then analyze treatment;
assess quality and value separately;
document uncertainty;
clearly communicate what is screening and what is a confirmed conclusion.
Chapter Summary
A diamond simulant looks like diamond but is not diamond material.
A synthetic diamond is not a simulant.
A treated natural diamond is not a simulant.
Material identity must precede natural/synthetic origin.
ISO 18323 and CIBJO provide a professional nomenclature framework but are not automatically the law of every jurisdiction.
The term synthetic must be tied to the specific synthesized material.
Appearance is useful for orientation but is not final identification.
RI, refraction, dispersion, density, hardness, and conductivity operate as combined identification axes.
The scratch test is not a professional method.
A thermal-only tester may have difficulty with moissanite, and a tester does not determine natural/synthetic origin.
A screening result such as refer is not a diagnosis.
A simulant is a legitimate product when the material is disclosed clearly and accurately.
Figure 64.1. Hierarchy of questions—material identity – origin – treatment – quality/value Visual AtlasFigure 64.2. Natural diamond, synthetic diamond, treated diamond, simulant, and composite—conceptual map Visual AtlasFigure 64.3. Screening versus identification—pass/refer/confirm logic Visual AtlasFigure 64.4. Decision tree for an unknown diamond-like stone Visual AtlasFigure 64.5. How CIBJO names a composite stone—doublet, triplet, and composite, components from the upper part downwards Visual Atlas
Sources for this chapter
Sources are primary or authoritative; the label in brackets gives the jurisdiction or source type.