Quartz is the most common mineral used in the crafting of jewellery, and has been so since the days of hallowed antiquity. Whilst most people recognise quartz as being a clear crystalline mineral it comes in a wide variety of forms. These stones exhibit such varied characteristics, that they were viewed as wholly distinct, and it is only recent scientific advancements which have revealed them all to be the same base mineral.
Quartz is the seventh hardest mineral on Mohs hardness scale, and this strength has allowed it to be cut and worked into a myriad of elaborate, enduring forms of jewellery over the centuries.
Below is a list of all of the forms which quartz can take, along with their particular characteristics and uses in antique and contemporary jewellery:
The purest form of quartz used in jewellery is known as “Rock Crystal” these silicon and oxygen crystals are translucent or completely clear. The clarity of these stones is the reason for the name “Quartz”, which derives from the ancient greek κρύος (kruos), which means “icy cold”, as they were so clear that some philosophers believed the mineral to be a form of permanent ice.
Rock crystal’s clarity makes it a perfect material for jewellery. Though it lacks the scintillation of diamonds its beauty when cut by a skilled lapidary is beyond question.
When rock crystal takes on a greyish hue it is known as smoky quartz, whereas white impurities turn it into milky quartz.
The purple variety of quartz is named Amethyst, and in ancient times it was considered to be one of the Cardinal Gems, five stones whose beauty and value surpassed all others. The root of the name amethyst is the greek “amethystos”, meaning “not intoxicated”. This was due to the legend that the clear stone had been coloured purple when the god Bacchus poured wine upon it, an act that supposedly enabled the amethyst to cure drunkenness.
Amethyst is far less rare than it was in ancient times, as large deposits were discovered in Brazil in the early years of the 19th century, but this abundance in no way detracts from the beauty of the stone.
This honey-golden variant of quartz is rare in nature, and most modern citrines are amethysts which have been heat treated to change their colour. Natural citrine has a cloudy, smoky appearance, whereas heat treated amethysts form lines inside the crystal, and can be easily distinguished.
Citrine was tremendously popular during the Victorian era, and was a favourite stone of Queen Victoria herself.
In certain conditions it is possible to find stones which have both amethyst and citrine colours. In these stones the golden and purple colours exist in bands, giving a two tone effect. Although this stone is technically named ametrine, after its two constituent colours, it is almost exclusively mined in bolivia, hence its trade name; bolivianite.
Rose quartz has a soft, cloudy pink hue and is most often opaque. Patterns within rose quartz are caused by tiny rutile needles, the same material which gives star sapphires and rubies their distinctive asterism.
The smooth surface of rose quartz takes a high polish, and its understated beauty is a gentler kind than some of its showier cousins.
The deep red carnelian is an opaque variety of quartz often cut en cabochon, but which is also used in intaglios and seals of great intricacy. Carnelian is so named after the latin carnis, meaning flesh, due to its blood red colouration.
It has been worked since ancient times by cultures across the world.
Agate is formed from layers of superheated quartz and chalcedony cooling at different rates. The slightest variation in conditions causes different impurities to be released into different layers, causing strange and vibrant combinations of colour. No two pieces of agate are the same, and its tremendous variety has earned it the fitting nickname “Earth Rainbow”.
Like carnelian, agate has been worked since ancient times, and is the most common hard carving material on earth. This means that there are an almost infinite variety of forms which agate has been sculpted into throughout the centuries, and each one bears the definitive stamp of the era in which it was made.
Onyx is named after the greek word ὄνυξ, meaning “claw”, and comes in both jet black and red varieties. Whilst some pieces of onyx are pure black or red, many have bands or waves of brilliant white laced through them. It is believed that the name derives from the fact that the white banding can resemble the growth of a fingernail.
Sardonyx is a variety of onyx which includes different shades of red banding or waves, known as “sards”.
Jasper is formed from granules of quartz and chalcedony, and like agate can exist in a huge variety of colours. One of the more interesting variants is bloodstone, which is a deep green, almost black, with flecks of bright crimson, like droplets of blood. This material has been used to make macabre imagery and memento mori pieces for centuries.
Tigers eye is a fascinating material with fiery golden and deep bronze layers which shift when the stone is turned. The tiny quartz crystals which have grown into these layers are interwoven, which means that as light hits them from different angles different waves of crystal catch the light.
Sometimes quartz will form with a single band which seems to move through the stone as it is turned. This is known as cats eye.
To find out more about precious stones, and their use in antique jewellery, take a look at the other articles in our advice centre.
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