What is Sardonyx – The August Birthstone

Sardonyx – The August Birthstone

Women in Ancient Rome wore adornments made of this August birthstone, Sardonyx, that is known to protect and give strength. Therefore, even warriors would carry Sardonyx to the battle field. 

Sardonyx is greatly used in astrology. Its beliefs have originated from ancient history and thus this gemstone holds value in the lives of many, even today.

Now Sardonyx is a Semi-precious stone. Why would anyone choose to possess a Semi-precious stone?

Well, semi-precious stones are cheaper ie.  not as expensive as precious stones. These have certain beliefs attached to it and they can be possessed regardless of the birthchart.  

Let’s understand this August Birthstone in detail.


Sardonyx stones are easily identified by their alternating dark and light bands of flat white, gray, red and brown colors. The veined gem, as it’s often called, is a colored variety of the onyx. Agate and 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 black to almost every color. 

Commonly, specimens of onyx contain bands of black and/or white Black onyx is perhaps the most famous variety, but is not as common as onyx with colored bands. Sardonyx encourages you to strive for a purpose, find meaning in your life. It has a focusing and soothing effect when coupled with meditation.

Formation and Chemistry

Sard forms from the deposition of silica at low temperature from silica-rich waters percolating through cracks and fissures in other rocks  The name sardonyx is from the greek ‘sard’, meaning reddish brown, and ‘onux’ meaning fingernail. Sardonyx forms from silicon dioxide as a variety of onyx and is a member of the chalcedony cryptocrystalline quartz family. Geologically, sardonyx contains alternating bands of sard and onyx, which is why the name. Sard is a dark orange or red or black in color and onyx is mostly black, although it can be any color. 

History and origins

Onyx was used in Egypt as early as the Second Dynasty to make bowls and other pottery items.  Use of sardonyx appears in the art of Minoan Crete, notably from the archaeological recoveries at Knossos. One famous locality for sard is Ratnapura, Sri Lanka. Sources also contain India, Brazil and Uruguay. It was also used at Harappa, one of the centers of the Indus civilization (c2300-1500BC), by the Mycenaean’s (1450-1100BC), and also by the Assyrians (1400-600BC). The Luc Yen region in northern Vietnam has produced this August birthstone in deep red, purple, pink, violet and violet-blue since the 1980s, and vivid blue spinels were found there in the 2000s.


Sardonyx can be traced back four thousand years, to Ancient Egypt. This stone was used to create cameos and intaglios. Women in Ancient Rome wore sardonyx necklaces with cameos of Venus in hopes of harnessing the power of goddess of love. It was common for soldiers to wear sardonyx rings and carvings containing images of Mars, the god of war, when they rode in battle as a means of protection.  It was stone famous for the use of seals, and signet rings that were used to imprint wax emblems on official documents, because the hot wax did not stick to the stone.


It is known as the stone of strength and protection, since ancient times. It is associated with courage, joy, communication and connection. People wear sardonyx to increase stability in marriages and partnerships. Sardonyx is an August birthstone, for zodiac signs Aries and Leo. They are known for their grounding energies as they work with the earth star and the root chakra. These stones are beneficial for jobs demanding extreme willpower and mental discipline.


It brings the wearer a lot of charisma and power. Sardonyx is particularly suitable for a type – slender, quick moving, and intellectually active. Unsurprisingly, it highlights and empowers these traits, and stops them from working against you, if out of control. On a similar note people working in creative fields will find this stone helpful in using its energies to think outside the box. These energies of the stone will inspire you to make better and more well-informed decisions because they will not only make you self-aware but will also open your eyes up to your surroundings.


Sardonyx is actually silicon dioxide, with a Mohs Hardness of 6.5 to 7, with a specific gravity of 2.55 to 2.70. It is cryptocrystalline quartz, consisting of fine intergrowths of the silica minerals quartz . The optical properties include a refractive index of 1.53 to 1.54, with a birefringence 0.008 to 0.010. The Crystal System of this gemstone is trigonal, luster being vitreous and silky. There is no cleavage, and fracture is uneven, conchoidal. 


Sardonyx is a durable stone however not recommended for prolonged, daily wear. It must be washed with warm soapy water and a soft brush.  An ultrasonic or steam cleaner may be used cautiously. Continuous exposure to heat or chemicals must be avoided while exercising or cleaning.

Famous Sardonyx

Gift of Milton Weil, 1929 contains a sardonyx cameo in a gold frame of the Emperor Augustus on the horns of a double-headed goat, 27 BCE -14 CE, kept in Metropolitan Museum of Art, New York, Public Domain.


Sardonyx is typically found naturally untreated, however it is not uncommon for its look to be achieved by staining agate. The inferior quality gems are treated with the iron oxide pigment to attain the bright deep orange red color while carbon is used to create the desired striped veins.

Identification of Sardonyx

Sardonyx stones are easily identified by their alternating dark and light bands of flat white, gray, red and brown colors.

For detailed practical identification you can check out this link: New Courses in Gemology (jkdiamondsinstitute.com)


Sardonyx makes a great gift for people born in August who want something more elegant than the traditional peridot or spinel birthstone. Readily available and relatively inexpensive, sardonyx makes an affordable addition to anyone’s collection., and has become a famous choice for jewelry. For enhancement, the gemstone can be dyed or stained to help improve its overall color and appearance. The most attractive sardonyx shows a high contrast between reddish layers of sard stone and white bands of onyx. It may be translucent or opaque, seldom showing flaws or fractures. Sardonyx is widely available and moderately priced in sizes up to 10 carats. The most common cut is cabochon, though it is popularly carved into cameos, intaglios, inlays, and brooches to emphasize the contrast between layers.

Learn more about the fascinating world of gems and gemology at JK