Chemical Formula SiO2
Color White, Black, Banded
Crystal System Hexagonal
Refractive Index 1.54 – 1.55
SG 2.63 – 2.65
Transparency Translucent to opaque
Double Refraction .009
Mineral Class Quartz (Chalcedony)
Onyx is an ancient gemstone, having been used in jewelry and as an ornamental gemstone for carvings since antiquity. Onyx has traditionally been one of the most important engraving and cameo gemstones, where its most common form was a black base with a white upper layer. Although still used a minor gemstone today, the significance and value of Onyx has been diminished as compared to ancient times.
When Onyx is banded black and white, it can be jointly classified as both Agate and Onyx. However, many require Onyx to have banding in roughly parallel lines, whereas other forms of Agate can have wavy or concentric forms of banding.
Onyx is usually cut into cabochons and beads, where it is mostly used in bracelets, necklaces, earrings, and rings. It is also an important cameo and intaglio stone, and carvings and small statues have also been cut from it.
Black Onyx – Solid black form of Onyx.
Onyx Agate – Banded variety of Onyx/Agate with parallel bands of black and white.Limestone Onyx, Mexican Onyx, or Onyx Marble – Travertine or Tufa that exhibits color banding from layer deposition. This material can be polished and dyed and used as an ornamental stone.
Green Onyx – Often refers to Chalcedony dyed a deep green color; may also refer to Agate banded light green and white. Sometimes also incorrectly used to describe green Onyx Marble (above).
Onyx Opal – Banded, dark colored Opal.
Rhodochrosite Onyx – Banded variety of Rhodochrosite (Rosinca).Black Onyx is often dyed. The banded white and black form is usually natural and not dyed.Sources of Onyx include India, Brazil, and Uruguay.Black Onyx can be similar to Black Diamond, though it is much softer and less lustrous. It is much harder than Jet. Black Onyx lacks the metallic luster of Hematite, but it can be very difficult to distinguish from Melanite Garnet and Schorl Tourmaline. Opal is the most colorful of gems. Its splendid play of color is unsurpassed, and fine examples can even be more valuable than Diamond. The play of color consists of iridescent color flashes that change with the angle at which the stone is viewed. This phenomenon is often called opalescence. The play of color may consist of large, individual flashes of color (known as schillers), or may be of tiny, dense flashes. The intensity and distribution of the color flashes is a determining factor in the value of an Opal.
Onyx TREATMENTS AND ENHANCEMENTS