Quartz Mineral Properties, Facts and Varieties

Contents 1. What is Quartz? 2. Quartz and Piezoelectricity 3. Rock Crystal Clear Quartz 4. Types of Quartz 5. Article Pictures 6. Shop Quartz

What is Quartz?

Quartz, which is composed of silicon and oxygen, is the second most common mineral in Earth's crust after feldspar. It can be found in almost every geological environment and is a component of virtually every rock type. It's also the primary constituent of most sand.

Because of its abundance and widespread distribution, quartz is the world's most diverse mineral in terms of varieties, colours, and forms. It can be found in sedimentary rocks as grains of sand and as crystals in igneous and metamorphic rocks.

Quartzite, which is composed almost completely of the mineral quartz, is produced through the metamorphism of sandstone.

Silicon dioxide, a chemical compound of silicon and oxygen, is found most commonly in nature as the mineral quartz. It exists in several crystalline forms and numerous cryptocrystalline forms.

Silicon dioxide is also known as silica.

The name 'quartz' is believed to come from the old German word 'quarz', which first appeared in 1530. In ancient Greece, quartz was known as 'krustallos', from 'kruos', meaning 'icy cold'. This may have come about because of the clarity of some quartz crystals.

Theophrastus, the ancient Greek philosopher and successor to Aristotle, believed colourless quartz crystals were a unique type of ice that wouldn't melt. 

Quartz Crystals and Piezoelectricity

Quartz crystals possess a unique property called piezoelectricity. This means they generate an electric charge when subjected to mechanical stress or pressure.

Quartz crystals vibrate at exceptionally precise intervals at a specific frequency when an electric current is applied.

The piezoelectricity produced by a quartz crystal enables electronic circuits to generate regular and accurate signals, which are essential for measuring time.

The frequency at which a quartz crystal vibrates is determined by its shape, size, thickness, and cut. The frequency can be adjusted by altering any of these properties.

Quartz crystals used in timekeeping devices vibrate at precisely 32,768 times per second.

Quartz was the first crystal to be used in radio transmission and was fundamental to the development of computers.

Rock Crystal: Clear, Colourless Quartz

Rock crystal is an alternative name for colourless quartz. Quartz is colourless and transparent to translucent when free from impurities, hence the term 'crystal clear.'

Impurities can produce a wide variety of colours, ranging from milky white to brown so dark that it can appear almost black.

Quartz exists in many different varieties and occurs in two main forms: crystalline, which has visible crystals, and cryptocrystalline, where the crystals are too small to be seen with the naked eye.

Coloured varieties of quartz tend to be translucent rather than transparent, and most have their own name. 

Inclusions in quartz are relatively common. Quartz with inclusions is often referred to as included quartz. Rutile and tourmaline are two of the most common mineral inclusions.

The optical properties of quartz led to its extensive use in lenses and prisms. It was once widely used in electronic components but has now been replaced with a synthetic alternative.

As well as having electrical properties, quartz is also resistant to heat. Being graded 7 on the Mohs scale of mineral hardness, makes it harder than many other natural minerals. It's therefore often used as an abrasive.

Despite its hardness, quartz is brittle, so it will break or shatter easily. In geology, hardness and toughness are not the same.

Hardness refers to a mineral's resistance to being scratched by another. Toughness, correctly known as tenacity, refers to its resistance to being bent, cracked, chipped or broken.

Different Types of Quartz

Agate
A translucent variety of chalcedony best known for being banded.

Amethyst
A purple variety of quartz whose colour is caused by iron.

Aventurine
A type of translucent quartz typically identified by its platy inclusions.

Bloodstone
Dark green chalcedony that often features red markings caused by inclusions of iron oxides, usually hematite

Carnelian
Reddish to rich orange-coloured quartz. A translucent variety of chalcedony. Sometimes called Cornelian.

Chalcedony
Chalcedony is a variety of microcrystalline quartz, white in its purest form. Most types of chalcedony have their own names, such as agate, bloodstone, or carnelian.

Chevron Amethyst
A combination of colourless or milky quartz combined with amethyst. Named for its chevron-like markings. Also known as Banded Amethyst.

Chrysoprase
Translucent apple-green variety of chalcedony whose colour comes from nickel.

Citrine
A relatively rare, yellow to yellowish-brown variety. Most commercial-grade citrine is heated amethyst

Included Quartz
Although some varieties, such as rutiliated quartz, have their own name, this group tends to be known collectively as included quartz.

Jasper
Cryptocrystalline variety of chalcedony with fine inclusions of varying amounts of other minerals and substances. These inclusions make Jasper opaque and are also responsible for its wide range of colours.

Miky Quartz (aka White Quartz/Snow Quartz)
White to greyish-white, translucent to opaque variety. Often occurs in the same deposit as rock crystal.
Onyx
Striped variety of agate with alternating black and white bands. The name 'Onyx' is widely misused.

Rose Quartz
Pink translucent stone with a massive crystal habit. Pink quartz, a slightly different variety, is far more scarce and forms individual crystals. Unlike rose quartz, it also fades when exposed to UV light. Individual crystals in rose quartz have never been found.

Rock Crystal
Colourless and transparent variety of quartz. The name came about during the late Middle Ages to differentiate this type of quartz from a newly produced colourless material known as glass. Glass was known as crystal or crystal glass.

Sard
Translucent light to dark brown coloured chalcedony. Until the Middle Ages, sard shared its name with carnelian. Gemstones with bands of white sard and chalcedony are called sardonyx.

Smoky Quartz
A translucent to transparent variety that occurs in various shades of brown.

Tigers Eye
This type of quartz, also known as tiger eye, has a rich golden-yellow colour caused by the presence of iron.

Article Pictures

The quartz crystals in this article are from our collection. The first image, the colourless quartz crystals, and last image are clickable and redirect to the original photo. 

Pop-up images: Colourless quartz: Courtesy of Ron Wolf. Rutilated quartz and quartzite: Courtesy of Stan Celestian. Chrysoprase: Courtesy of James St. John. Sard: Taken by Stone Mania. Sardonyx: Courtesy of Captain Tenneal.