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Natural black onyx gemstone jewellery
With its deep, subterranean hue and storied lineage, black onyx stands as one of history’s most resonant personal gemstones. A cherished variety of cryptocrystalline quartz, it rose to prominence as the heart of Victorian sentiment and mourning jewellery: a gentle, tactile comfort designed for solace and quiet reflection. Beyond its emotional legacy, its velvety midnight polish defined the sharp, geometric silhouettes of the Art Deco era. Today, black onyx continues to inspire with its quiet, resolute sophistication, offering exceptional durability and a profound connection to strength, memory, and individual character.
Colour spectrum
Jet black, porcelain white, reddish brown
Pictured: Petite Quatrefoil Black Onyx Necklace
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SiO₂
Microcrystalline quartz · Chalcedony
Microcrystalline silicon dioxide, SiO₂, belonging to the cryptocrystalline chalcedony family of quartz. It forms a dense, interlocking fibrous aggregate structure precipitated from silica rich fluids inside volcanic vesicles and sedimentary host rocks. Highly valued for its sleek midnight finish, uniform aggregate density, and smooth vitreous to waxy lustre that absorbs and reflects light with a quiet, understated elegance.
6.5 to 7
on the Mohs scale
Rating a dependable 6.5 to 7 on the Mohs Hardness Scale, black onyx possesses remarkable structural toughness due to its microscopic, tightly interlocked quartz fibres. Possessing no directional cleavage, it resists chipping and scratching, making it an ideal choice for daily wear jewellery, personal protective talismans, and sentimental heirlooms that endure over generations.
Natural onyx is defined by crisp, strictly parallel layers of contrasting hues. While earth born varieties include sardonyx with its warm ribbons of reddish brown and white, the quintessential expression features contrasting strata of jet black and porcelain white. Historically prized as “true” or “Arabic” onyx, specimens showcasing a delicate white upper layer set against a deep black foundation offer unmatched graphic refinement.
| Feature | Featured at UgemsBlack Onyx | Black Star Diopside |
|---|---|---|
| Mineral Species & Family | ChalcedonyMicrocrystalline Quartz family. | Pyroxene Group mineral |
| Mohs Hardness | 6.5 to 7 / 10Highly durable for daily wear. | 5.5 to 6 / 10Softer; best suited to protective settings. |
| Transparency | Semi translucent to opaqueEdges show soft light transmission. | Opaque to deep semi opaqueDark brownish black to jet black body colour. |
| Signature Optical Character | Displays quiet light absorption with a sleek, waxy to vitreous lustre. | Asterism (4 Rayed Star) & Silky SheenReveals a striking four rayed star under direct lighting. Unlike six rayed star sapphires (60°), its four distinct rays intersect at non orthogonal angles (75° and 105°), created by aligned microscopic magnetite needles within its crystal matrix. |
| Ideal Gem Cutting | High domed cabochons, sleek architectural tablets, and tailored vintage cushion cuts. | Exclusively polished cabochonHigh domed cuts to perfectly centre and reveal the floating star. |
| Ugems co. Positioning | Exclusively FeaturedLoved not for flashy fire, but for its subterranean depth and historic mystery: a velvety, architectural canvas radiating timeless sophistication. | In Design at UgemsTreasured for its magical optical secret, direct light awakens a striking four rayed star upon its ink black surface: a celestial moment captured within stone, reminiscent of a solitary star dancing in the midnight sky. |
Learn more about Our Materials or find ideas in The Art of Gifting.
