Onyx
This article is about the mineral. For other uses, see Onyx (disambiguation).Onyx is a cryptocrystalline form of quartz. The colors of its bands range from white to almost every color (save some shades, such as purple or blue). Commonly, specimens of onyx available contain bands of colors of white, tan, and brown. Sardonyx is a variant in which the colored bands are sard (shades of red) rather than black. Pure black onyx is common, and perhaps the most famous variety, but not as common as onyx with banded colors.
Sardonyx (banded agate). The specimen is 2.5 cm (1 inch) wide.It is usually cut as a cabochon, or into beads, and is also used for intaglios and cameos, where the bands make the image contrast with the ground. Some onyx is natural but much is produced by the staining of agate.
The name has sometimes been used, incorrectly, to label other banded lapidary materials, such as banded calcite found in Mexico, Pakistan, and other places, and often carved, polished and sold. This material is much softer than true onyx, and much more readily available. The majority of carved items sold as 'onyx' today are this carbonate material.[1]
Technical details Chemical composition and name SiO2 - Silicon dioxide Hardness (Mohs scale) 7 Specific gravity 2.65 - 2.667 Refractive index (R.I.) 1.543 - 1.552 to 1.545 - 1.554 Birefringence 0.009 Optic sign Positive Optical character Uniaxial
Etymology
Onyx comes through Latin from the Greek onyx meaning 'claw' or 'fingernail'. With its fleshtone color, onyx can be said to resemble a fingernail. The English word 'nail' is cognatewith the Greek word.[2]
Historical usage
Onyx from Australia.
Onyx from Brazil.The Beinecke Rare Book and Manuscript Library at Yale University was originally planned to be coated in green onyx. However, there wasn't sufficient green onyx in the world to build such a structure, so that the designers used marble. Onyx was known to the ancient Greeks and Romans.[3] Use of sardonyx appears in the art of Minoan Crete, notably from the archaeological recoveries at Knossos.[4] Onyx was used in Egypt as early as the Second Dynasty to make bowls and other pottery items.[5] It is also mentioned in Exodus 25.
Black onyx with bands of colors.
Onyx
Onyx is a cryptocrystalline form of quartz. The colors of its bands range from white to almost every color (save some shades, such as purple or blue). Commonly, specimens of onyx available contain bands of colors of white, tan, and brown. Sardonyx is a variant in which the colored bands are sard (shades of red) rather than black. Pure black onyx is common, and perhaps the most famous variety, but not as common as onyx with banded colors.
It is usually cut as a cabochon, or into beads, and is also used for intaglios and cameos, where the bands make the image contrast with the ground. Some onyx is natural but much is produced by the staining of agate.
The name has sometimes been used, incorrectly, to label other banded lapidary materials, such as banded calcite found in Mexico, Pakistan, and other places, and often carved, polished and sold. This material is much softer than true onyx, and much more readily available. The majority of carved items sold as 'onyx' today are this carbonate material.[1]
| Chemical composition and name | SiO2 - Silicon dioxide |
| Hardness (Mohs scale) | 7 |
| Specific gravity | 2.65 - 2.667 |
| Refractive index (R.I.) | 1.543 - 1.552 to 1.545 - 1.554 |
| Birefringence | 0.009 |
| Optic sign | Positive |
| Optical character | Uniaxial |
Etymology
Onyx comes through Latin from the Greek onyx meaning 'claw' or 'fingernail'. With its fleshtone color, onyx can be said to resemble a fingernail. The English word 'nail' is cognatewith the Greek word.[2]
Historical usage
The Beinecke Rare Book and Manuscript Library at Yale University was originally planned to be coated in green onyx. However, there wasn't sufficient green onyx in the world to build such a structure, so that the designers used marble. Onyx was known to the ancient Greeks and Romans.[3] Use of sardonyx appears in the art of Minoan Crete, notably from the archaeological recoveries at Knossos.[4] Onyx was used in Egypt as early as the Second Dynasty to make bowls and other pottery items.[5] It is also mentioned in Exodus 25.
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