Natural, Synthetic, and Simulated Gemstones: What the Terms Mean

Shopping for gemstones or reading old jewelry listings, you will run into a confusing set of labels: natural, synthetic, lab-created, simulated, imitation, treated, enhanced. These words have specific meanings, and mixing them up is one of the most common sources of misunderstanding among new collectors. The short version is that a synthetic stone is the real material made in a lab, a simulant only looks like the real material, and a treated stone is natural material that has been altered after mining.

Natural Gemstones

A natural gemstone formed through geological or biological processes without human involvement, apart from cutting and polishing. A natural sapphire crystallized in the earth over a very long period, was mined, and was then cut. Natural stones often contain small inclusions, growth lines, or color zoning that record the conditions they formed in. These features are one of the main ways laboratories tell natural stones from lab-grown ones.

Synthetic and Lab-Grown Gemstones

A synthetic gemstone has essentially the same chemical composition, crystal structure, and physical properties as its natural counterpart, but it was grown in a laboratory. A synthetic ruby is genuine corundum with chromium, just like a natural ruby. It is not fake, but it is not natural either. The terms “lab-grown,” “lab-created,” and “laboratory-created” are used for the same idea.

Synthetic gems have a long history. In the early 1900s, the French chemist Auguste Verneuil developed the flame fusion process, which melts powdered chemicals and lets them crystallize into synthetic corundum. Later methods include:

Flux growth, where crystals grow slowly from a molten chemical solution, used for synthetic emerald and ruby.
Hydrothermal growth, which imitates the way quartz and emerald grow from hot water in nature. Most quartz used in electronics is grown this way.
HPHT and CVD, two methods used to grow diamond. HPHT recreates high pressure and temperature, while CVD builds diamond layer by layer from carbon-rich gas.

Because synthetics share the same properties as natural stones, simple tests such as hardness or streak cannot separate them. Laboratories rely on magnification, spectroscopy, and other specialized instruments.

Simulated and Imitation Gemstones

A simulant, or imitation, is a different material that is used to look like a particular gem. It does not share the same chemistry or properties. Common examples include:

Cubic zirconia, a lab-made material widely used to imitate diamond.
Synthetic moissanite (silicon carbide), which is also used as a diamond simulant. It is a synthetic material in its own right, but a simulant when it stands in for diamond.
Glass, which has been used to imitate almost every colored gem for centuries.
Plastics and resins, often used to imitate amber, coral, or turquoise.

Simulants can often be detected with basic observation. Glass, for instance, is usually softer than the gem it imitates and may show rounded gas bubbles or swirl marks under a loupe.

Treated and Enhanced Gemstones

A treated gemstone is natural material that has been altered after mining to improve its color or clarity. Treatment is extremely common and is not necessarily a problem, as long as it is disclosed. Some widespread examples:

Heat treatment is routinely used on sapphire and ruby to improve color and clarity, and it turns some amethyst into citrine.
Oil or resin filling is common in emerald to make surface-reaching fractures less visible.
Dyeing is widely used on agate, howlite, and other porous stones.
Irradiation is used to produce the blue color in most blue topaz on the market.

Treatments affect how a stone should be cared for. An oiled emerald, for example, should not go into an ultrasonic cleaner, and some dyes fade or bleed with time.

Composite Stones

Some stones are assembled from more than one piece. A doublet glues a thin slice of gem material to a backing, and a triplet adds a clear protective cap on top. Opal doublets and triplets are common because they make thin seams of precious opal usable. These are legitimate products when described accurately, but they need gentle care because the adhesive layers can fail with heat or soaking.

Why Accurate Labels Matter

In many countries, trade rules require sellers to disclose when a gem is synthetic, simulated, or treated, and the words “natural” or “genuine” should not be used for lab-grown material without a clear qualifier. For collectors, accurate labels matter because they affect care, value, and the story a specimen tells. If you are unsure what you own, a qualified gemologist or accredited gem laboratory can test it. Steiner Collectables explains the terms but does not test or authenticate stones. For more background on the qualities that make a material a gem in the first place, see What Makes a Gemstone?