I have talked before about the birthstone list published in 1912 by the American National Retail Jeweler’s Association (now Jewellers of America (JA)). This is the list we use today apart from a few changes over the years. One of those areas of change relates to the August birthstone. In 1912, sardonyx was listed as the main August gemstone, with the peridot as an alternate. Over the years, the peridot became the sole birthstone for March and the sardonyx disappeared. In 2016, the JA and the American Gem Society added the spinel as an August gemstone. However, some lists have the three August gemstones, like that of the American Gem Trade Association and the American Gem Society. The UK’s National Association of Goldsmiths still lists the peridot and the sardonyx.
Sardonyx, like bloodstone, the disappearing March gemstone, is not a commonly used gemstone today. It also belongs to the quartz family of gemstones and has been used for centuries in signet rings, cameos, seals, and lockets, but it is no longer a fashionable gemstone.
Quartz is a complex family of gemstones. One part of the family are chalcedony quartz, which are defined as fine grained quartz with a fibrous microstructure, also called cryptocrystalline. They are translucent, have a dull or waxy lustre, and usually display some type of banding, though it can be quite indistinct. Those with distinct banding are called agates. We know onyx today as black but onyx is actually a parallel banded chalcedony agate with, usually, bands of black or dark brown and white. When the parallel bands are reddish brown or dark orange and white, the stone is called ‘sardonyx, derived from two words, ‘sard’ and ‘onyx’. ‘Sard’ is said to be named after the ancient Persian city of Sardis, where this reddish brown/dark orange and white layered agate was mined.
There is a bit of confusion about sard and carnelian, another chalcedony quartz. Carnelian is an beautiful orange colour but as the colour becomes darker and more brown, it is then described as sard. The only difference between sard and carnelian is the colour. Often, any cameo or intaglio with orange to brown and white layers is referred to as sardonyx
The most ancient of the August birthstones, sardonyx is a combination of two types of chalcedony (cryptocrystalline quartz): sard and onyx. Bands of brownish red to brown to dark orange sard alternate with typically white or black layers of onyx. In ancient times, mineral chalcedony. Agateand onyx are both varieties of layered chalcedony that differ only in the form of the bands: agate has curved bands and onyx has parallel bands. The colors of its bands range from white to almost every color. Commonly, specimens of onyx contain bands of black and/or white.
Sardonyx is a variant in which the colored bands are sard (shades of red) rather than black. Black onyx is perhaps the most famous variety, but is not as common as onyx with colored bands. Artificial treatments have been used since ancient times to produce both the black color in “black onyx” and the reds and yellows in sardonyx. Most “black onyx” on the market is artificially colored
SHIELD SARDONYX AND 15ct GOLD LOCKET
locket (that has sold)