Ever wondered what Onyx is?

Finely Banded Black & White Onyx

THE GEMSTONE ONYX

Onyx is a gemstone whose description can have several connotations. Its most accepted gemstone definition describes a solid black Chalcedony, or a banded or layered black and white Chalcedony. The term Onyx is occasionally used to described any engraved stone with a solid color base, or it may describe any banded gemstone with parallel banding. In its solid black form, Onyx is the most traditional black gemstone.

Chemical Formula SiO2
Color White, Black, Banded
Hardness 7
Crystal System Hexagonal
Refractive Index 1.54 – 1.55
SG 2.63 – 2.65
Transparency Translucent to opaque
Double Refraction .009
Luster Vitreous
Cleavage Indiscernible
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.
VARIETIES
FALSE NAMES
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).
Sources of Onyx include India, Brazil, and Uruguay.
SIMILAR GEMSTONES
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.

– See more at: http://www.minerals.net/gemstone/onyx_gemstone.aspx#sthash.mrJU2apW.dpuf

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