02 · Ask what has changed
Natural does not necessarily mean untreated.
Heat can change colour; dyes add colour; coatings alter a surface; oils, resins or glass can fill fractures. These processes have different implications for appearance and care. Ask which treatments are known and which are uncertain.
For a brightly coloured stone, ask whether it has been dyed or coated. Strong colour alone does not prove either. Avoid using solvents, heat or scratch tests to try to settle the question yourself.
Further reading: GIA: introduction to gem treatments ↗ (opens in a new tab)
Citrine is a useful example: heating some amethyst produces citrine. A photo alone cannot reliably establish a particular piece’s treatment history.
Read the citrine comparison →A glassy appearance is not a verdict.
Manufactured glass can resemble gemstones, but natural minerals can also have a glassy lustre. Natural obsidian is itself volcanic glass. Ask for the actual material name instead of treating “glass” as a complete description.
Further reading: GIA: glass and other imitations ↗ (opens in a new tab)
Visible bubbles may prompt a closer examination, but natural gems can contain fluid inclusions with gas bubbles. A single photograph or visual clue is not a universal authenticity test.
Further reading: GIA: inclusions in gemstones ↗ (opens in a new tab)
Explore the Obsidian guide →Translate the trade name.
A commercial name may describe a colour, mixture or marketed product rather than a mineral species. Ask: “What mineral or material is this?” Then keep both the trade name and the seller’s explanation in your notes.
Our Caribbean Calcite page is an example of keeping a collection label separate from a precise identification. An appealing name does not establish where an individual specimen was mined.
Read the Caribbean Calcite label notes →Read what the report actually says.
A GIA coloured-stone identification report identifies the material, whether it is natural or laboratory-grown, and detectable treatments. A seller’s decorative authenticity card is not automatically the same kind of examination.
If a laboratory report is offered, check it with the issuing laboratory and compare its photograph, dimensions and description with the item. Ask about anything that does not match. Consider independent examination when a costly purchase depends on an uncertain claim.
Further reading: GIA: sample coloured-stone reports ↗ (opens in a new tab)
Further reading: GIA Report Check ↗ (opens in a new tab)
03 · Make the decision
Pause before you pay.
- Ask for photos of the actual piece, including its back, base and any damage, in ordinary light.
- Check dimensions and weight rather than judging size from a close-up.
- Confirm the total price, delivery arrangements and seller’s return terms.
- Keep the listing, written answers and receipt with your specimen record.
- If an important question remains unanswered, wait or choose another piece.
Our practical suggestion: set a comfortable hobby budget and choose for your collection, rather than relying on promised rarity or future resale value.