Quartz: Meaning, Characteristics and Jewellery

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The quartz stone is one of the most commonly used gemstones in jewellery and one of the few coloured stones you’ll find in almost every jewellery shop. In this guide, you’ll learn about the meaning of quartz, its properties and characteristics, the different varieties and colours (rock crystal, amethyst, citrine, rose quartz, smoky quartz, agate and others), treatments, its use in jewellery, how to look after the stone and its production in Brazil. At the end, there is an FAQ section covering the most common questions.

Pedra de quarto - variedade calcedonia — Bedrock – a variety of chalcedony

What is quartz?

Quartz is a mineral composed of silicon dioxide (SiO₂). According to mineralogy sources, it is the second most abundant mineral in the continental crust, after feldspars. It is one of the main components of granite and other igneous rocks, occurs in sedimentary rocks (it is the main constituent of sand) and is common in metamorphic rocks.

Well-formed crystals can grow to be very large. In Brazilian deposits, a study by the United States Geological Survey (USGS) cites crystals weighing up to 40 tonnes, and many deposits containing crystals weighing between 1 and 5 tonnes.

Silica (SiO₂) exists in various mineral forms, known as polymorphs: quartz, tridymite, cristobalite, coesite and stishovite. Each form is stable under specific conditions of temperature and pressure. Common (alpha) quartz changes to beta quartz at 573 °C, and the change reverts when the stone cools.

Video about quartz

Pedra de Quartzo - Caracteristicas, Cores e Variedades

Properties and characteristics of quartz

Composition: silicon dioxide, SiO₂;
Crystal system: trigonal (the crystals have six faces, but are not hexagonal);
Hardness: 7 on the Mohs scale;
Density: approximately 2.65 (2.66, according to the GIA);
Refractive index: 1.544 to 1.553;
Lustre: vitreous;
Fracture: conchoidal, without cleavage;
Colour: colourless, white, purple, pink, yellow, brown, black and others;
Transparency: ranging from transparent to opaque, depending on the variety.

Quartz retains its properties over time. With a hardness of 7, it withstands everyday scratches well, but as it is not particularly tough, it can chip at the tips and thin edges, so care should be taken to avoid knocks.

The meaning of quartz

The meanings attributed to quartz stem from tradition and belief, rather than scientific evidence. The word ‘crystal’ comes from the Greek krystallos, meaning ‘ice’, as the ancients believed that rock crystal was ice frozen so deeply that it never melted. Since ancient times, rock crystal has been cut into spheres used for divination, and even today quartz is associated with mystical and energy-based beliefs, such as the idea that rose quartz brings love and harmony. None of this has been proven.

In jewellery, certain varieties feature in the gemstone calendar: amethyst is the birthstone for February, citrine is the birthstone for November, and rose quartz is the gemstone for the fifth wedding anniversary, according to the GIA.

Quartz in jewellery

Quartz is a good choice for jewellery because it is affordable, has a hardness of 7 and comes in many colours. Large stones can be bought at prices well below those of other gemstones, and quartz is durable enough for everyday wear, provided you avoid knocks. Both men and women wear quartz jewellery, and it can be found in any cut: cabochon, faceted, tumbled and drilled beads.

Principais Gemas e Pedras Preciosas — Main Gems and Precious Stones

Quartz is also carved into decorative objects, such as paperweights, animal sculptures, seals and carvings, and into items such as spheres and bowls. As well as in jewellery, quartz crystals are used in watches: quartz vibrates when an electric current is applied, and this vibration keeps time in quartz watches.

Varieties of quartz

There are two main groups of quartz, which are further divided into varieties with specific names.

1. Macro-crystalline quartz

Macrocrystalline quartz includes rock crystal, amethyst, citrine, rose quartz, smoky quartz, blue quartz, prasiolite (green) and varieties with a cat’s-eye effect, such as falcon’s eye and tiger’s eye. It is generally transparent to translucent and forms with crystals larger than those of cryptocrystalline quartz.

2. Cryptocrystalline quartz

Crypto-crystalline quartz is formed of microscopic crystals, which in most cases cannot be seen even under a magnifying glass. When mixed with moganite (another polymorph of silica), it is called chalcedony. Chalcedony includes agate, chrysoprase, heliotrope (bloodstone), jasper and carnelian. Strictly speaking, ‘chalcedony’ usually refers to the single-coloured, paler variety, which is generally bluish. This group is generally opaque or translucent and may display various colours within the same specimen.

Principais variedades de quartzo — Main varieties of quartz

Colours and types of quartz crystals

The colour of macrocrystalline quartz varies greatly, but colourless quartz is by far the most common, followed by white or milky quartz. Purple (amethyst), pink, brown and black (smoky quartz) are also common. Generally speaking, the deeper the colour, the higher the value. The main varieties are:

Rock crystal: colourless quartz, the most common type;
Amethyst: quartz ranging in colour from lilac to purple. Studies link the colour to iron (Fe⁴⁺) and natural radiation. It is one of the most highly prized varieties;
Rose quartz: ranging from almost white to medium-dark pink. It is usually translucent, with tiny inclusions that give it a cloudy appearance, and the finest colours are found in larger stones. Stones with well-aligned inclusions may display a six-pointed star (asterism);
Smoky quartz: ranging from yellowish-brown to almost black. The colour is linked to aluminium impurities and natural radiation;
Citrine: yellow to orange. Natural citrine is rare and lighter in colour, and most of the ‘citrine’ sold is heated amethyst. Most comes from Brazil, mainly from Rio Grande do Sul;
Milky quartz: white and more opaque, due to tiny inclusions;
Rutilated quartz: rock crystal containing (golden) rutile needles;
Agate: a cryptocrystalline variety, with bands of various colours.

Clarity, brilliance and cut

The highest-quality quartz is transparent – that is, it allows light to pass through unimpeded – and ‘clear’, with no inclusions. In translucent quartz, the light passes through more dimly. As quartz is abundant, there is little reason to choose stones with visible inclusions, except for those that define the gem’s character, such as cat’s eye, hawk’s eye and rutilated quartz. The lustre of the crystals is vitreous, and in cryptocrystalline forms it is usually waxy to opaque, although it may be vitreous.

Clear quartz is usually faceted, whilst translucent or opaque quartz is cut into cabochons or carved. As colour is distributed unevenly within the crystals, the cut is chosen to enhance the colour, and it comes in many standardised sizes and shapes.

Treatments and synthetic quartz

Many coloured gemstones are enhanced. The most common treatments for quartz are:

Heating: when heated, amethyst turns yellow, orange or brown and is sold as citrine;
Irradiation: radiation can darken the stone – for example, producing smoky quartz – and is combined with heat treatment to achieve specific colours;
Dyes: used on agates and other chalcedonies;
Impregnation or coating: with wax, clear resin or other materials, to enhance the colour, lustre and stability.

Rock crystal is generally untreated. Synthetic quartz (grown in a laboratory) has the same composition and structure as natural quartz and is abundant; it often comes in colours that do not occur in nature or that are too intense to be natural. Naturally coloured quartz may display bands of colour. Clarity alone does not distinguish natural from synthetic quartz, and therefore valuable specimens should be accompanied by a gemmological laboratory report.

How to look after quartz jewellery

Cleaning: use warm water with mild soap and a soft cloth, and dry thoroughly. Before using an ultrasonic cleaner, check the item for cracks, repairs and settings;
Temperature: avoid sudden changes in temperature. Intense heat can alter the colour of varieties such as amethyst;
Light: as a precaution, do not leave coloured quartz pieces exposed to direct sunlight for long periods;
Impact: quartz can chip at the edges and tips, so avoid knocks and store the pieces separately from harder gemstones (such as diamond, sapphire and ruby), which may scratch it.

Uses and production of quartz in Brazil

The highest-quality crystals are used in the electronics and optics industries, whilst those of lower quality are used in abrasives, ceramics and metallurgy. Quartz is also used in the manufacture of glass, cosmetics, watches, computers and in the construction industry, as it is abundant. Since the late 1970s, laboratory-grown quartz has largely replaced natural quartz in electronics.

According to the National Mining Agency (2014 Mineral Summary), the states that produce quartz crystal are Bahia, Goiás, Mato Grosso, Minas Gerais, Santa Catarina, Pará and Espírito Santo, and most of the production comes from small-scale miners. Brazil is the sole producer of natural quartz blocks with piezoelectric properties, mainly in Goiás, Minas Gerais and Bahia, and holds around 95 per cent of the world’s reserves, estimated at the time at 78 million tonnes.

Sources consulted

Frequently Asked Questions

What is quartz?

It is a silicon dioxide (SiO₂) mineral, the second most abundant in the continental crust. It comes in many colours and varieties, such as rock crystal, amethyst, citrine, rose quartz and agate, and is widely used in jewellery.

What is the significance of the quartz stone?

Traditionally, quartz is associated with clarity, protection and energy, whilst rose quartz is associated with love. These meanings stem from popular belief rather than scientific evidence. The word ‘crystal’ comes from the Greek krystallos, meaning ‘ice’.

What are the properties of quartz?

Hardness 7 on the Mohs scale, density approximately 2.65, refractive index 1.544 to 1.553, vitreous lustre, conchoidal fracture and no cleavage. The crystal system is trigonal.

Is quartz a gemstone?

It is a gemstone widely used in jewellery, but, as it is abundant, it is generally more affordable than stones such as diamonds, rubies, sapphires and emeralds.

What are the main varieties of quartz?

There are macrocrystalline minerals, such as rock crystal, amethyst, citrine, rose quartz, smoky quartz and prasiolite, and cryptocrystalline minerals (chalcedony), such as agate, carnelian, chrysoprase, jasper and heliotrope.

Are amethyst and citrine types of quartz?

Yes. Amethyst is purple quartz, and citrine is yellow to orange quartz. Most of the citrine sold is heat-treated amethyst, and natural citrine is rare.

Can quartz be worn in jewellery every day?

Yes, but be careful. With a hardness of 7, it is quite scratch-resistant, but it can chip at the tips and along fine edges, so it needs to be protected from knocks.

How can you tell whether quartz is natural or synthetic?

It is difficult to tell with the naked eye, because synthetic quartz has the same composition and structure as natural quartz. Colours that are too vivid to be natural are a warning sign. For high-value purchases, ask for a gemmological laboratory report.

How do you clean quartz jewellery?

Use warm water, mild soap and a soft cloth. Avoid sudden changes in temperature and excessive heat, and before using an ultrasonic cleaner, check the item for any cracks, repairs or settings.

Where is quartz produced in Brazil?

According to the ANM, the states that produce quartz crystal are Bahia, Goiás, Mato Grosso, Minas Gerais, Santa Catarina, Pará and Espírito Santo. Brazil is the only producer of natural quartz blocks with piezoelectric properties.

Written by Willy Sievert

Editor of Bahia.ws since its founding in 2009. Based in Salvador, he travels frequently across the Northeast and all of Brazil to keep the guides up to date. Learn more about Willy Sievert →

Published on 24/09/2023 · Updated on 11/10/2026