1st - Gold 
January 
February 
March 
April 
May 
June 
July 
August 
September 
October 
November 
December 
Capricorn - Garnet 
Aquarius - Amethyst 
Pisces - Aquamarine 
Aries - Diamond 
Taurus - Emerald 
Gemini - Pearl 
Cancer - Ruby 
Leo - Peridot 
Virgo - Blue Sapphire 
Libra - Opal 
Scorpio - Topaz 
Sagittarius - Tanzanite 
Chalcedony Gemstones – Properties, Origins, Treatments and Buying Guide
Chalcedony is a highly admired gemstone in the quartz family, valued for its soft, translucent appearance and range of pastel colours. Unlike vividly saturated gemstones, chalcedony exhibits beauty in its subtle uniformity, smooth texture, and gentle glow.
In this guide we examine chalcedony from a professional gemmological and commercial perspective, covering its physical properties, crystal structure, treatments, origins, and how to identify high-quality stones.
What is Chalcedony?
Chalcedony is a microcrystalline variety of quartz composed of silicon dioxide (SiO₂). It forms in cryptocrystalline masses rather than visible crystals, giving it a smooth texture and translucent appearance. Its pastel colours, which include blue, pink, grey, and white, make it highly desirable in cabochons and carvings.
Mineral Composition
Chalcedony has the chemical formula:
SiO₂
It is composed primarily of:
Silicon
Oxygen
The microcrystalline structure consists of interlocking quartz fibres, giving chalcedony its translucence and waxy lustre.
Mineral Family and Crystal System
Chalcedony belongs to the quartz (silicate) family.
Its crystal system is trigonal, but its microcrystalline nature prevents visible crystal formation, resulting in a smooth, uniform texture ideal for cabochons and beads.
Optical and Physical Properties
Chalcedony combines a gentle translucence with uniform colour, making it highly valued for carvings, jewellery, and ornamental objects.
Lustre
Waxy to vitreous, giving a soft glow.
Transparency
Translucent to semi-transparent; top-quality stones show uniform colour and gentle light diffusion.
Refractive index
1.530 – 1.540, providing soft optical clarity.
Specific gravity
2.58 – 2.64, typical of quartz varieties.
Colour Range
Chalcedony occurs in soft pastel colours:
Blue
Pink
Grey
White
Lavender
Green
Uniformity of colour and translucence greatly affects value.
Mohs Hardness and Durability
Chalcedony has a Mohs hardness of 6 – 7, making it suitable for pendants, earrings, beads, and moderate-wear rings. It is generally tough but can chip if struck sharply.
Treatments
Most chalcedony is naturally coloured. Some stones are dyed or heat-treated to enhance uniformity, which should always be disclosed by reputable sellers.
Care and Cleaning
Avoid harsh chemicals and ultrasonic cleaners.
Use warm water, mild soap, and a soft cloth or brush.
Store chalcedony separately from harder gemstones to prevent scratches.
Major Origins
Major sources of chalcedony include:
Brazil
India
Turkey
Madagascar
United States (California, Oregon)
Namibia
Frequently Asked Questions
Is chalcedony a natural gemstone?
Yes, chalcedony occurs naturally and is widely used in jewellery and carvings.
What colours does chalcedony come in?
It occurs in pastel shades of blue, pink, grey, white, lavender, and green.
Is chalcedony treated?
Some stones are dyed or heat-treated to enhance colour, but natural chalcedony is also widely available.
Is chalcedony suitable for daily wear?
Yes, with a Mohs hardness of 6–7, but care should be taken to avoid hard impacts.
How can I tell if chalcedony is real?
Look for uniform translucence, smooth texture, and waxy to vitreous lustre.
Does chalcedony fade in sunlight?
Properly coloured chalcedony is stable and does not fade under normal sunlight exposure.
Where does the finest chalcedony come from?
Brazil, India, Turkey, and Madagascar are known for high-quality chalcedony.
Can chalcedony be scratched easily?
It is moderately hard, but can be scratched by harder quartz or gemstones like sapphire.
Is chalcedony suitable for rings?
Yes, but rings should be worn with care to avoid chipping.
Can chalcedony be cleaned with ultrasonic machines?
No, avoid ultrasonic and steam cleaners; use warm water and mild soap instead.