Chalcedony is a cryptocrystalline form of silica, composed of very fine intergrowths of the minerals quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, whilst moganite is monoclinic.
Chalcedony has a waxy luster, and may be semitransparent or translucent. It can assume a wide range of colors, but those most commonly seen are white to gray, grayish-blue or a shade of brown ranging from pale to nearly black.
There are variety of chalcedonies but the most popular in vintage Jewelries is the onyx and especially the black one. Yet, you can find other chalcedonies in jewelries such as Agate (Sardonyx), Heliotrope (called also Bloodstone for its color) and the Carnelian.
To learn more on the different types of Chalcedony

BIRTHSTONE AND ANNIVERSARY
Onyx is the birthstone associated with July and December. The Bloodstone associated with March but is an alternate birthstone for February also. Agate (Sardonyx) is an alternate birthstone for August, May and September. is an alternate birthstone for August.
The Onyx is the stone used to celebrate the 7th wedding anniversary.
For more details on birthstone and it's meaning

Please have a look at our wonderful rings with this gemstone

ORIGIN OF NAME
The term chalcedony may derive from the ancient Greek port Chalkedon (in modern English usually spelled Chalcedon), which is known today as the Kadıköy district of Istanbul. Carnelian is derived form the Latin word meaning "cornelian cherry". Chrysoprase is derived from the Greek words "chrysos" and "prase", which combined mean "golden leak".

HISTORY
Agate is one of the earliest gemstones and have been used during the stone age (20,000BC to 16,000BC). Agate, carnelian and chrysoprase were used by the Egyptians before 3000 BC. Carnelian was often used by the Romans to make cameos. The prophet Mohammed even wore a carnelian seal. During Roman empire, Idar and Oberstein provided agate and jasper. These German towns are no longer a source of chalcedony, but remain known for their skills with processing the stones. Chalcedony is a common stone. It is formed in cavities, cracks and is formed where silica-rich waters percolate through sediments and rocks - especially where there is volcanic origin.

GEMSTONE POPULRITY IN VINTAGE PERIODS:
During the Early Victorian Period, chalcedony was often used to make cameos from jasper and agate. Bloodstone was also used in the Victorian Period. During the late Victorian Period, onyx was used for making rings. During the Art Deco Jewelry Period, black onyx, chrysoprase and cornelian agate were widely used materials.

LEGENDS
Bloodstone was believed to preserve the owner's health and protect them against deception. Chrysoprase was believed to strengthen vision and relieve internal pain. Carnelian was believed in the 13th century to give the owner courage for battle. In Volmar's thirteenth-century novel, Steinbuch, created the legend that a thief may escape his execution by putting chalcedony in his mouth.

HARDNESS
With a hardness of 7.5, on the Moh's Scale [link], chalcedony is hard enough for daily wear. Exposure to cleansing agents, even mild soaps, can ruin a chalcedony's finish. Rings should always be removed prior to washing one's hands. Likewise, ultra-sonic cleanings can remove the finish and ruin the stone.

Don't miss our amazing jewelry with this gemstone

TECHNICAL DATA
Crystal system: Trigonal
Cleavage: None
Refractive Index 1.53 - 1.54
Specific Gravity (1): 2.58 - 2.64, some jasper 2.9

(1) SPECIFIC GRAVITY
The specific gravity is the ration of the density of an object when compared to water. In the simplest testing, it is simply the weight of a mineral compared to its volume. The volume of the stone is measured by the amount of water in displaces.

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