What is Chalcedony?

Chalcedony is a type of quartz but unlike quartz which is composed of crystals, Chalcedony is composed of sub-microscopic fibres. There are several different types of Chalcedony, characterized by the way the fibres form into different layers.

It is thought that Chalcedony is named after an ancient town at the Bosporus.

Types of chalcedony include:

•    Agate – in a variety of colours
•    Bloodstone – dark green with red spots
•    Carnelian – brownish red to brownish orange
•    Fire agate – brown body with iridescent hues
•    Jasper – a variety of colours apart from black
•    Moss agate – green, black or brown inclusions
•    Onyx – parallel layers of different colours – often black and white
•    Sardonyx – parallel brown bands alternate with black or white


Records show that they were used for cameos in ancient times.

Onyx has been stained in order to improve its colour since Ancient Egyptian times.

Onyx, in particular was popular with the Romans who carved patterns in the stones to give a raised print.

Agates have been collected from Germany since 1548.


The various varieties of chalcedony have different qualities attributed to them. It was thought that agate would cure insomnia, bloodstone would stabilize blood flow, (the spots were thought to be the blood of Jesus Christ) and Chrysoprase was thought to improve eyesight and relieve internal pain.


Chalcedony can usually be cleaned in a steamer or ultrasonic cleaner, but the colour of chalcedony can sometimes change in extreme heat. Acids should be avoided and it should be stored away from other jewellery.

It is best to clean Chalcedony in warm, sudsy water, then rinse with clear water, wipe dry and leave to dry on a towel.

Caring for Chalcedony (Summary)

•    Store away from other jewellery
•    Clean in warm, soapy water
•    Rinse with clear water and leave on towel to dry


Chalcedony measures 6 – 7 on the Mohs hardness scale and has a density of 2.58 – 2.64.