Seylan Gems & Jewelry
Some gems are bought for an effect that a single head-on photo cannot hold. A star, a cat’s eye, a color change, or a shift from blue to gray as you turn the stone are different causes. The listing should name the effect and the species.
Specifications
Typical published ranges used in gemology. Specific gravity below matches our carat calculator default where applicable. (SG 4.00)
| Star | Asterism, usually six rays on a cabochon |
|---|---|
| Cat’s eye | Chatoyancy, one ray on a cabochon |
| Color change | A different hue in different lights, as in alexandrite |
| Pleochroism | Different colors down different crystal directions |
| Play of color | Opal’s moving flashes, not the same as diamond fire |
| Proof | You should see the effect in person or in an honest moving view |
Both come from fine parallel needles or tubes. The cut has to be a cabochon aligned to those needles. A star has several rays crossing. A cat’s eye has one. Sharpness and centering are the quality, together with body color.
Our star sapphire and cat’s eye guides go into the version we sell. Glass can imitate either effect. Species and “natural” are separate claims.
Alexandrite is the reference for color change: a different hue in daylight than in warm indoor light. Turning the stone in one light is not the test. Changing the light is the test.
Iolite, tanzanite, and tourmaline are strongly pleochroic. Turn them and the color shifts even under the same lamp, because you are looking down a different crystal direction. A good cut chooses the direction you want to wear. That is not a color-change stone, and it should not be described as one.
The needles are in the crystal. The cutter reveals them. High heat can destroy rutile silk and the star with it. A painted star on the back of a cabochon is an imitation and has to be sold as that.
No. A weak shift is still color change and is worth less than a strong one. Look at both lights before you pay for the word.
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Sapphire
Ruby
Alexandrite
Emerald
Padparadscha
Aquamarine
Spinel
Garnet
Peridot
Tourmaline
Tanzanite
Citrine
Quartz
Chrysoberyl
Apatite
Topaz
Amethyst
Lolite
Zircon
Sinhalite
Cats Eye
Opal