how to facet
gemstone main cabochon creation
min data

Mineral: quartz
Gem: sard agate (cryptocrystalline)
Size: 10 mm x 13 mm
Carat: 3.95 ct
Cut: cabochon
Origin: unknown
General Info: Agate (achates) was named from the river Achates, now the Drillo, in Sicily, where the stone was first identified. It is cryptocrystalline quartz (micro crystals) usually with a banded pattern (although not always).
Additional Information
Sard (or sometimes "sardonyx") is a brown to orange version of banded agate. In most onyx, if there is banding, it is mostly parallel and straight. This is partially what the name "onyx" implies, concentrically banded agate is rarely called onyx. If the agate bands run straight or nearly straight the material is called onyx.

Sardonyx is used to cut cameos. When the original rough is parted along the lines instead of across them, it results in alternating layers of color. White or light colored material is oriented to the top and the darker color below. In the case of sardonyx, the white or cream color band is the upper most, and the orange or brown band is located below.

When the top (light colored band) is carved it begins to show the darker material below. Hence the shadows are created by letting the dark color show through.

The diagram to the left shows the general steps in creating a cameo type blank. Two layers of bands of agate remain.

The top band is then cut or carved to reveal the color below and this creates the pattern.