How to identify a gemstone by its colour
Colour is one of the fastest clues to a gemstone’s identity, but it is only one property. This guide explains how to use hue, tone and visible features to narrow possibilities, what checks to run next, and when to seek further testing.
Quick facts
- Mineral
- Ruby and sapphire: corundum
- Cause
- Chromium colours ruby red
1. Start by describing the colour precisely
Note the hue (red, green, blue, etc.), the tone (light to dark) and the saturation (dull to vivid). Record whether the colour shifts when you tilt the stone and whether it looks the same in daylight and under indoor light. A careful written note or a clear photo from a scanner or phone helps later comparison and recognition.
2. Compare appearance to known gems
Match your description to common gems with similar colours. For red stones, check whether the red matches known red gems; remember: Ruby and sapphire: corundum. Look at inclusion patterns under magnification—some gems show characteristic needle-like, fingerprint or twinned crystal inclusions that help identification.
3. Use simple physical checks after colour
Colour alone cannot confirm identity or value. Check crystal habit and cleavage with careful observation: a crystal face or triangular cross-section points to particular mineral groups. Use a loupe, take a clear photo and, if available, a handheld scanner to capture surface features. Avoid destructive tests. If you must go further, ask a lab for refractive index or specific gravity tests rather than relying on colour.
4. Understand common colour look-alikes
Many gems share colours: a red could be garnet, spinel, tourmaline or corundum; a green could be tourmaline, emerald or peridot. Check for pleochroism (colour change on different angles) and for the presence of characteristic inclusions and crystal form. Keep in mind the stone’s context—was it found among rocks or cut and set as a gem—which affects likely identification and worth.
5. Red stones and why they get that colour
When you see a vivid red, consider the cause of the colour. Chromium colours ruby red. That chemical cause is a diagnostic clue when combined with other tests such as crystal habit and optical properties.
6. Final checks before accepting an ID
If colour, inclusions and crystal features point to a likely gem, confirm with non-destructive lab tests or a trusted finder or app if you need speed. Keep records: photo, where the specimen came from, and any tester readings. This record supports later appraisal and assessment of value or worth.
7. Using Rock Identifier
If you want an automated check after you have done the steps above, try Rock Identifier to compare photos and get suggestions.
Common questions
- Can I identify a gemstone by colour alone?
- No. Colour gives a starting point but is not definitive. You should also check crystal features, inclusions, pleochroism and, if needed, lab tests. Colour combined with these clues improves recognition and reduces misidentification.
- How useful is a photo or scanner for identification?
- A high-quality photo or scanner image is useful for recording hue, tone and visible inclusions and for sharing with a finder or specialist. Lighting and white balance affect perceived colour, so include a daylight photo and a note about lighting conditions.
- What if a red stone could be several gems?
- Compare inclusion type, crystal habit and optical effects. Remember that Ruby and sapphire: corundum. If chromium is present, it affects colour—Chromium colours ruby red—but lab tests or specialist inspection are needed to confirm.