Trillion-cut faceted black onyx gemstone, available in 5 mm and 6 mm. Dense, uniform black with a vitreous luster. Selected for geometric and minimalist jewelry in sterling silver.
Piece Details
| Mineral |
Black onyx (chalcedony, dyed agate variety) |
| Dimensions |
5×5 mm or 6×6 mm depending on chosen variant |
| Shape and Cut |
Trillion (faceted triangular), with crown and pavilion facets |
| Finish |
High polish |
| Hardness |
6.5–7 Mohs — suitable for rings, earrings, and pendants; resistant to daily wear |
| Origin |
Material selected in wholesale gemological market |
| Treatment |
Dyed black — standard and historically documented process for commercial black onyx; color is stable and permanent |
| Piece Type |
Available in 2 sizes (5 mm and 6 mm) |
The trillion cut and why it works in black
The trillion cut is a triangular cut with three curved or straight sides and a varying number of crown and pavilion facets (generally 31–44 in classic versions). In black materials like onyx, the trillion acts differently from the oval or brilliant cut: instead of multiplying internal light flashes, it creates crisp reflection planes and geometric edges that emphasize shape over brilliance.
Why black onyx is always dyed
Commercial black onyx is almost universally chalcedony (microcrystalline quartz) dyed using a sugar and sulfuric acid impregnation process that has remained essentially unchanged since Pliny the Elder described it in the 1st century AD. Natural chalcedony is rarely solid black—it is usually gray, beige, or banded—so black dyeing is the industry standard, not an exception.
In crystal tradition, black onyx is associated with protection and grounding—the stone said to act as an energetic shield and stabilize during times of change. Shared for educational purposes, not as medical advice.
What setting it works for
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Sterling silver claw setting (geometric solitaire) — the trillion's triangle is especially prominent in settings that do not obscure the vertices; pointed claws reinforce the piece's geometry.
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Geometric ring or statement earring — the 6 mm trillion has enough presence for a modern solitaire ring; the 5 mm is ideal for minimalist earrings or earring pairs.
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Triangular pavé or multistone composition — black trillions combine well with white diamonds or colored gemstones to create geometric contrasts in designer jewelry pieces.
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Wire wrap — possible; the trillion requires wrapping at all three vertices or around the girdle to avoid stressing the angles.
Onyx in jewelry history
Black onyx has been valued in Western jewelry since Roman antiquity, where it was used to carve cameos and seals (the black on white of banded chalcedony creates the ideal contrast for relief).
The symbolic properties attributed to minerals belong to cultural and historical traditions. Shared for educational purposes, not as medical advice or a substitute for professional care.
How to distinguish genuine onyx from black glass
Black glass is the most common substitute for onyx. To distinguish them: genuine onyx (chalcedony) has a hardness of 6.5–7 Mohs and is not scratched by a steel blade; glass (5.5 Mohs) does yield. Under magnification, onyx may show a very fine microcrystalline texture; glass is completely amorphous and homogeneous. When touched to the cheek, a large mass of onyx feels colder than glass.
Frequently Asked Questions
Is it genuine onyx?
Yes. It is genuine chalcedony (microcrystalline quartz) with standard dyeing treatment. The hardness of 6.5–7 Mohs distinguishes it from imitation black glass (5.5 Mohs).
Does the black color fade over time?
The dyeing of black onyx is stable and permanent under normal use and care conditions. It does not fade with water or light. It is the same industrial process documented since Roman antiquity.
See also: faceted gemstones · handmade silver rings · sterling silver earrings.
