Sardonyx is a mineral with a hardness of 7 out of 10 on the Mohs scale of mineral hardness [?]. These Trigonally structured gems are made of silicon dioxide, their full chemical compound being SiO2.

Sardonyx is a gem variety of reddish-brown colored sard with white or black banded chalcedony or onyx, used to make cameo with the raised black, red, or brown background. It is an example of a layer stone subvariety of Chalcedony, which in turn is a cryptocrystalline variety of Quartz.


Layer stones are multi-layered materials used in the art of gem-carving and engraving, also called glyptography. Usually this material is cut from agates with even parallel layers, a lighter layer above a darker one. Brazil supplies the best raw material, usually two-layered, but sometimes three-layered ones are seen. Some masterpieces are cut out of five-layered material. Engravings in multi-layered and curved agates are rare.


The combination of a black base and a white upper layer is called "onyx," different from the true onyx and onyx marble. In the case of "sard-onyx" the base is brown. While sard is dark reddish-brown, sardonyx is sard with white bands, or white with brown bands.


There are also "eye agate" varieties of banded agate, onyx, chalcedony, or sardonyx, in which the delicate colored bands are circularly arranged in such a way that they resemble an eye.


Sardonyx with varied prefixes, is usually mistaken for catalinite, and mistakenly applied to carnelian and sard.

The specific gravity [?] for Sardonyx is 2.61, it's refractive index [?] is 1.53-1.54, and it's double refraction [?] is 0.004.

History

Sardonyx is considered the gem symbol of the apostle John.


The Ring of Polycrates, a legendary ring, according to Pliny, was made of sardonyx (according to Herodotus an emerald ring) belonged to Polycrates the ruler of the Aegean isle of Samosa in the fifth century BC.

Industrial Usages

Sardonyx is often cut cabochon and tumbled. Mostly sardonyxes are carved as cameo, in which the relief being worked in the white layer with raised black, red or brown background.


A bluish-gray tint is produced by the use of the thin white upper layer, that is, by the distribution of light and the translucency of the black/brown background. Such layer stones are sometimes called "niccolo" These stones are in demand for seal rings and for engravings of coat-of-arms and initials. Engravings which have a negative picture, as used for a seal, are called "intaglios"; those with solid, raised images, are called "cameos".


Layers in agate, as required for this work, are often not found in nature in the colors of onyx, carnelian, or sard. Therefore such stones are mostly dyed. The dyed and natural stones have the same names.


Sardonyx, along with other stones with nearly flat bands, such agate, onyx, sardonyx, opal, shells, jet, rock crystal, giant conch, helmet shell, are considered suitable materials for cameos, a translucent layered gemstone generally composed of two layers (or more) and colors. The top layer has a raised figure or a design carved on it, while the second layer with other colors forms a background.


It is also used for engraved gemstones, an exquisite production of the lapidary arts of miniature sculptures, monogram, design, portrait, or inscription known as engraved gems. Most often used stones were agate and sardonyx for a two-color effect.

You May Also Like...

Bloodstone

Bloodstone: Bloodstone is a member of the Chalcedony group. Why is it called Bloodstone? Well because in polished and rough form this gem / mineral looks like blood, on a stone. (see photo) Bloodstone is sometimes referred to as Plasma or Heliotrope. Heliotrope is a birthstone for March. The name plasma is used to define a bloodstone with yellow inclusions, and not red ones.Despite its relative hardness (7 o (read full)

Amethyst

Amethyst: Amethyst is the most coveted stone in the quartz group, and it is sometimes confused with beryl. It is usually found layered with milky quartz, and its color varies from purple to violet. It is sometimes sold as Ametrine, but this is actually a combined variation of 2 gems; Amethyst and Citrine. Amethyst like Agate Chalcedony can be found in geodes. There are many types of synthetic Amethyst aro (read full)

Agate Chalcedony

Agate Chalcedony: Agate Chalcedony differs from other Chalcedony in that it often has distinct banding. In fact some slices of Agate may appear to have banding similar to that of tree rings. Due to its porous nature it is often colored (by humans) black, red, green, or blue to further increase its visual appeal. Agate Chalcedony is found in Brazil, China, Germany ,Hungary, Mexico, Uruguay, the United States, and (read full)

Milky Quartz

Milky Quartz: Milky Quartz is a milky white translucent to opaque variety of crystalline quartz of somewhat greasy luster. It is the commonest variety found in pegmatites and hydrothermal veins. The color is generally caused by numerous bubbles of gas and liquid in the crystal. The milky color is caused by small cavities filled with numerous small fluids and CO2 in liquid condition. It is used as a gemstone, a (read full)

Aventurine

Aventurine: Aventurine is a quartz mineral that is most often used to crave ornate animal or spiritual figures. Aventurescence is a term used to describe the shimmering of this stone that is caused by mica inclusions. The color is almost always green, however sometimes it is blue, or green with hints of blue, or brown. Aventurine is ideal for the carving of figures, but not the best material in the world for (read full)

Tags

Terms

Double Refraction or dr is the ability of a mineral to separate a refracted ray of light into 2 rays. If held over an image or text it will display the object 2x its original size.

Mohs Scale of Mineral Hardness is the standard used to categorize a mineral's ability to resist scratching. It gets its name from Friedrich Mohs, the German geologist who first created the scale.

RI or Refractive Index defines light's ability to move through the mineral or in a general sense, any material.

SG or Specific Gravity is the ratio of the weight of any substance to that of pure water at temperature of 3.98°C(39.2°F) and standard atmospheric pressure. This is important to note when actively seeking these minerals in the wild. Minerals with a higher SG will settle below material with a lower sg over time.