How can I tell a dyed agate, aura quartz, heated citrine, lab-grown quartz or glass?
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Some treatments are easy to see and some cannot be detected without a laboratory. Dye usually shows as color that does not occur in nature or color concentrated in cracks; metallic and iridescent "aura" coatings on quartz show as a surface film that scratches and wears at edges; turquoise is often impregnated with wax or polymer; and most citrine on the market is heated amethyst, which a buyer usually cannot tell from natural citrine by eye [1][2][3]. Lab-grown quartz and glass need tests or a reliable seller. This page goes through each treatment common in the decorative crystal trade, what you can check yourself, and what to ask a wholesaler.
Why this matters for a crystal or decor seller
Treated material is a large share of what moves through the decorative trade: tumbled stones, points, spheres, clusters and beads bought by the bag or the flat. Treatment is not wrong in itself. Many treated stones are attractive, inexpensive and sold honestly. The problem comes when a treated stone is sold as natural, because the buyer pays for something they are not getting. GIA states that treatment disclosure is "necessary and legally required for anyone selling a gem," including consumer-to-consumer sales [1], and the FTC's Jewelry Guides require disclosure of treatments that are not permanent, create special care needs, or significantly affect value (16 CFR 23.24) [4]. What that means for the words you use on a label or listing is set out on what you may legally call it.
Treatment by treatment
| Treatment | What it is (source) | Stones you will meet it on | What you can check | Detectable by eye? |
|---|---|---|---|---|
| Dyeing | Color introduced into porous or fractured stone [1][3] | GIA names howlite, chalcedony, quartz, turquoise, lapis lazuli, nephrite jade and coral among dyed materials [1] | Color not found in nature for that stone; color concentrated in cracks, pits and along banding | Often. Smith and McClure say dye is readily detectable with magnification, and an unnatural hue "alone proves the presence of dye (such as with agate)" [3]. Dye in turquoise "may not always be detectable" [3] |
| Surface coating, including "aura" quartz | Metal oxides applied by vapor deposition; GIA notes quartz is sometimes coated "to create colors rarely seen in natural quartz" [1] | Clear quartz points and clusters sold as "aura," "angel aura," "titanium" and similar trade names | Metallic or iridescent sheen; scratches, worn coating at edges and facet junctions, trapped bubbles [3] | Usually. Smith and McClure say metallic or iridescent coatings are readily recognized because they do not occur naturally [3] |
| Heating amethyst to citrine | Heat converts purple amethyst to yellow or orange; GIA says "most citrine is the result of heating" [2] and that amethyst geodes "are often heated to become giant citrine 'cathedrals'" [5] | Citrine points, clusters, geodes and tumbled stones | Very little without a lab | Usually not. Smith and McClure say heat treatment of such gems "is typically undetectable" without spectrometry [3] |
| Impregnation and stabilizing | Porous stone permeated with polymer, wax or plastic for durability [1] | Turquoise especially; also some opal and other porous stones [1][3] | Ask the supplier; stabilized turquoise is widely sold as such | Sometimes. Wax impregnation of turquoise is typically detected with a hot point and magnification, a test for a laboratory or gemologist [3] |
| Filling | Glass, resin, wax or oil in surface-reaching fractures or cavities [1] | Fractured stones in general | Flash of color or differing luster along cracks under a loupe | Often, by "a qualified gemologist using magnification" [1] |
| Irradiation | Exposure to an artificial radiation source to change color [1] | Various colored stones | Nothing at home; ask the supplier | No |
| Lab-grown (synthetic) | Made in a laboratory; "laboratory-grown" or "synthetic" may be used only when the product has essentially the same optical, physical and chemical properties as the natural stone (16 CFR 23.25(c)) [4] | Quartz in various colors; many gem species | Nothing reliable at home | Usually not; needs a laboratory |
| Imitation, simulant and glass | A different material made to look like the stone | Glass and other materials made to look like natural stone, often under invented trade names | Few reliable home checks; ask in writing what the material is | Rarely with confidence; a lab can tell |
Stones the sources read for this page do not cover in detail
Two items on most decorative-trade caution lists are not covered in the sources read for this page:
- Reconstituted turquoise, made from turquoise powder or fragments bound into a block. GIA's treatment overview and the 2002 treatment chart describe impregnation and the proprietary Zachery treatment of turquoise, which reduces porosity "and sometimes enhance[s] the color" [3], but not reconstitution [1][3].
- Glass and slag sold as obsidian or under trade names. No source read for this page gives a test.
For both, this page gives no home test. Ask the supplier in writing what the material is, and send an expensive or doubtful piece to a laboratory (getting a specimen tested).
A buyer's check, in order
- Ask what the stone is and whether it has been treated, before price is discussed. Write down the answer.
- Check the color against the species. Bright blue, pink or purple agate is dyed, since an unnatural hue proves dye [3]; howlite in turquoise blue is dyed howlite [1]. Strongly metallic or rainbow quartz is coated.
- Look at the cracks and pits with a 10x loupe. Dye collects there.
- Look at the edges and points. Coatings wear first at edges and facet junctions [3].
- Compare a lot. Identical color across hundreds of tumbled stones, or the same "natural" citrine in every tray, points to treated color.
- Treat citrine as heated unless the seller can document otherwise, since GIA says most citrine is heated amethyst [2].
- Keep the invoice and the supplier's description with your stock records.
Labeling what you sell
You do not need to avoid treated stones. You need to name them. A clear label might read "Quartz, coated (sold as 'aura quartz')," "Agate, dyed," "Citrine (heated amethyst)," "Turquoise, stabilized," or "Howlite, dyed blue." The FTC's Jewelry Guides also bar describing a manufactured product as "real," "genuine" or "natural" (16 CFR 23.27) and require a lab-grown or imitation stone's name to carry a qualifier such as "laboratory-grown," "imitation" or "simulated"; the Guides say "faux" alone is not adequate [4]. If a coated, dyed or impregnated stone needs special care (no soaking, no harsh cleaners, no heat), say so: 23.24 makes it unfair or deceptive to fail to disclose a treatment that "creates special care requirements for the gemstone" [4]. That matters for stones customers may put in water; see crystals in drinking water.
What to expect from a wholesaler
A good wholesaler tells you, in writing on the invoice or price list, which stones are dyed, coated, heated, irradiated, stabilized, reconstituted, lab-grown or imitation. If an invoice says only "assorted crystals," ask for a breakdown before you sell any of it. If a supplier will not disclose treatment in writing, you cannot disclose it to your own customers, and you carry the risk. How to choose and check suppliers is on who to buy from, and the FTC wording rules are on what you may legally call it.
References
- Gemological Institute of America, *An Introduction to Gem Treatments*, Robert Weldon, undated web page, read October 2026. https://www.gia.edu/gem-treatment
- Gemological Institute of America, *Is citrine treated?*, FAQ page, undated, read October 2026. https://www.gia.edu/gia-faq-treated-citrine
- Christopher P. Smith and Shane F. McClure, *Chart of Commercially Available Gem Treatments*, Gems & Gemology, Vol. 38, No. 4, Winter 2002. https://www.gia.edu/dam/migrated-assets/docs/doc1/Chart-of-Commercially-Available-Gem-Treatments.pdf
- Federal Trade Commission, *Guides for the Jewelry, Precious Metals, and Pewter Industries*, 16 CFR Part 23 (sections 23.24, 23.25 and 23.27; source 83 FR 40667, August 16, 2018), eCFR, up to date as of October 19, 2026. https://www.ecfr.gov/current/title-16/chapter-I/subchapter-B/part-23
- Gemological Institute of America, *Citrine Gemstone*, gem encyclopedia page, undated, read October 2026. https://www.gia.edu/citrine
