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History & Introduction


Onyx is an ancient gemstone, which was used for jewelry and as an ornamental gemstone for carvings purposes. Onyx has traditionally been one of the most important engraving and cameo gemstones with the most common form the black base with a white upper layer. Though, onyx is a minor gemstone now, but the significance and value of the stone has diminished as compared to ancient times.

Onyx is black and white banded agate (cryptocrystalline or chalcedony quartz). But it is different from onyx marble, which is limestone. The banding of onyx is parallel and consistent. Some varieties of onyx differ in color like sard onyx has a brown base and white upper layer, cornelian onyx has a red base and white upper layer, and Niccolo onyx consist of a thin upper layer, permitting the black base color to show through as grey or blue.

Onyx name is derived from the Greek word "onux", which means fingernail; this could be due to a Greek legend, in which Eros mischievously cut the fingernails of Aphrodite with an arrowhead whilst she slept, and the gods turned the clippings into stone. Onyx was cut and carved as a gemstone by the Ancient Greeks and Romans in cameos. Intaglio etchings (negative relief engravings) were also created with onyx. These carvings presented the banding of onyx.

Recognize - Onyx is easily recognized by its black base and white upper layer with parallel banding, but, related to sard onyx the base is brown and cornelian onyx consist of a red base. It is difficult to find out when the material is a single color and is easily distinguished from agate when seen in the rough, showing visibly parallel and banding consistently.

Availability - Onyx is available in countries all over the world, including Argentina, Australia, Brazil, India, Botswana, Madagascar, Mexico, Myanmar (Burma), Pakistan, Sri Lanka, Uruguay and the USA.

Usages - Onyx is usually cut into cabochons and beads and then it is mainly used in earrings, bracelets, rings and necklaces. It is also an important intaglio stone, and cameo and small statues and carvings are also cut from it.

Buying Guide

Color - Onyx has a black base and white upper layer, but may contain bands of various other colors between these layers. In gemstones, onyx may come in single color. In case of sard onyx, the color is brown to the base layer, cornelian onyx has a red base layer and niccolo onyx consist of a thin upper layer, allowing the black base layer to show through as grey or blue. Number of onyx gemstones are totally black.

Clarity and Lustre - Onyx consists of waxed to dull luster and is typically opaque.

Cut and Shape - Because it has its bands of color, onyx is often carved into beautiful cameos which increases the banding. It is even cut into glossy cabochons and even in faceted. Onyx gemstone is even drilled to make beads or pendants.

Treatment - Onyx is usually dyed to enhance its color and produce a uniform hue. These processes were used many years. A black color is achieved with the use of concentrated honey or sugar solution after heated sulphuric acid treatment.

Gemological Characteristics:

Chemical Formula SiO2 Silicon dioxide
Crystal Structure Trigonal, microcrystalline aggregates
Color Black based with white upper layer; various colors
Hardness 6.5 - 7
Refractive Index 1.530 - 1.540
Density 2.58 - 2.64
Cleavage None
Transparency Opaque
Double Refraction or Birefringence Up to 0.004
Lustre Waxy to dull
Fluorescence Varies according to bands: Partly strong; yellow, blue-white
Mineral Class Quartz (Chalcedony)

Classification:

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