Unraveling the mysteries of quartz, from ancient times to modern times

Quartz is one of the most common materials in the world – and one of humanity’s oldest fascinations. From ancient myths to modern science, quartz has played a role in virtually every aspect of human development – ​​and it’s a beautiful one at that.

But have you ever wondered what goes on behind the sparkling gemstone at the end of your necklace? Join us on a journey through geology, chemistry, electronics – and a little bit of parrotfish poop.

The gemstone that is everywhere

For a stone that is so ubiquitous in jewelry, you might be surprised at how rare quartz actually is is not. Because it is made almost entirely of oxygen and silicon – the two most abundant elements on Earth by mass – finding the ingredients to form the mineral is a breeze.

What may be more difficult is creating the right environment for it. “Most quartz forms form in igneous rocks or in environments with geothermal water,” explains Addison Rice, geologist, environmental engineer and PhD candidate in paleoceanography and geosciences at Utrecht University, in an article for the International Gem Society.

“Quartz is formed in igneous rocks when magma cools. Just as water turns to ice, silicon dioxide will crystallize as it cools. Slow cooling generally allows the crystals to grow larger,” she continued. “Quarter that grows in a similar way from silica-rich water forms. Silicon dioxide dissolves in water, like sugar in tea, but only at high temperature and pressure. When the temperature or pressure drops, the solution becomes saturated and quartz crystals form.”

Fortunately, there are two things that Earth has a lot of: water and magma. The result, therefore, is a crust on the planet that is about an eighth of a quartz in size: billions and billions of silicon dioxide molecules, all built into stacks of tetrahedrons to create the sparkling gemstones we know, love, and happily pay for.

So where is it all?

If 12 percent of the Earth’s continental crust is made of quartz, you might wonder why we don’t stumble over chunks of quartz every day. Well, in fact we are: beach sand in particular is made up mostly of quartz, which has eroded over the centuries into smaller and smaller particles under our feet (unless you’re in Hawaii – the famous white sand there is made of poop).

Close-up photo of grains of sand

Close-up photo of grains of sand.

Image credits: Jeff Holcombe/Shutterstock.com

Of course, there is a chance that you are looking for quartz in larger chunks than a grain of sand. That’s not a problem: “It is present in many igneous and metamorphic rocks, is a major constituent of granitic pegmatites, and a major constituent of sandstones,” explains Craig R. Glenn, professor of earth sciences in the Department of Geology and Geophysics at the University of Hawaii.

Rock crystal quartz can be found virtually all over the world, he wrote, with particularly notable formations in the Alps, southeastern Brazil, Madagascar and Japan. In the US, it’s best to look at Hot Springs, Arkansas or Little Falls and Ellenville, New York, he advised.

However, if you want a specific type of quartz – smoky or an iridescent hue – you may need to look elsewhere. And that’s because…

Where do the colors of quartz come from?

Basic quartz has a simple recipe: silicon and oxygen. It consists of exactly these two elements and forms a simple, translucent quartz that is so clear that it is easy to understand why the ancient Greeks confused it with water.

They “assumed that quartz crystals were frozen so hard that they would not melt,” the Smithsonian National Museum of History explains on their website. “They called the crystals ‘krystallos,’ their word for ice and the origin of our word ‘crystal.’ Crystals were really the original ‘crystals.’

But adding even a little bit of another element can create a variety of vibrant colors. Amethyst, for example – which you may not realize is quartz, but certainly is – owes its purple hue to the presence of iron, irradiated by gamma rays from the rock surrounding the gemstone. However, heat the stone above 440°C and you will get a sunny yellow citrine.

A clump of ametrine - a predominantly purple quartz with a visible yellow line through the center

You can even find quartz that has solidified halfway through the process. Half amethyst, half citrine, the result is known as ametrine.

Some types of quartz are not so distinctive: strawberry quartz looks like this because of the large particles of hematite, or lepidolite, or muscovite, or piemontite, or pretty much anything else that ends up in the rocks that looks enough like strawberry seeds. Some are So especially that it took millennia before we could decipher what was going on: rose quartz has been used since 7000 B.C. used in jewelry, but that was only at the beginning of the 21st century.st century that various spectrometry methods revealed what gives the rock its pink hue.

The perpetrator? A mineral that none of the researchers had seen before, but which was similar to a very rare aluminum borate silicate mineral called dumortierite. It is currently called dididumortierite.

Chalcedony

While most of the quartz we’ve seen so far wouldn’t look out of place on an engagement ring or pendant, there’s another entire branch of the mineral’s family tree that might not seem all that precious to you at first glance.

“Some quartz varieties, such as amethyst, citrine and rose quartz, are cut from single crystals, but more are polycrystalline. This means that a stone is composed of many interlocking crystals,” explains gemologist Pat Daly in an article for Gem-A, the Gemmological Society of Great Britain.

“Chalcedony is a quartz gemstone composed of very small crystals that are indistinguishable from each other with a loupe or a standard gemological microscope,” Daly writes.

The result is a rock that looks nothing like gemstones – things like the opaque nickel green of chrysoprase, or the earthy chaos of jasper and bloodstone. One of the most recognizable forms of chalcedony is agate: it “occurs as nodules, often in spaces that were once bubbles in volcanic rock,” Daly explains, giving it its nearly ubiquitous banding patterns.

beige-pink agate disc on a black stand with ribbons

A piece of agate kept in the Muséum de Nantes, showing the rock’s distinctive ribbon pattern.

“It grows inward from the walls of the cavities as fibrous quartz crystals,” Daly writes. “The fibers radiate from germination points and form a series of domes that compete for space as they grow. Structural striations, parallel to the advancing growth surfaces, are always present, even if the color bands are absent.”

The power of quartz

People have always liked shiny things, and quartz has never been an exception. “People in the earliest times believed in the magical powers of quartz,” notes the Gemological Institute of America. “Ancient Roman, Egyptian and Greek civilizations used quartz crystals as powerful talismans.”

Quartz appears in mythologies and traditions as wide-ranging as the Aboriginal peoples of Australia and the prehistoric peoples of Ireland; “The Romans used rose quartz as a seal to signify ownership,” the Institute explains, “and the Egyptians believed the stone could prevent aging.”

Photo of rose quartz vase on gray background

A rose quartz vase from the Qing dynasty, China, 18th century

Image credits: The Metropolitan Museum of Art, gift of Heber R. Bishop, 1902, (CC0 1.0)

But what may surprise you is that the belief of all these groups in the power of quartz crystals – well, that wasn’t the case. precisely wrong, if you take the term ‘power’ literally.

We’re not going to talk about centering your chakras or finding your birthstones here – but it’s certainly true that quartz can produce a certain type of energy. Specifically, it involves electrical energy: squeeze the stone – or to use more scientific terminology, expose it to mechanical stress – and you can move a small electrical charge through it.

It is called piezoelectricity – the name comes from the Greek ‘piezein’, or ‘squeeze’ – and was originally discovered in 1880, by Pierre Curie (pre-Marie era) and his brother Jacques.

People had known before that something strange was going on when you crushed quartz, but no one had been able to prove it – and even after the brothers confirmed and named the phenomenon, it turned out to be so complex that no real progress was made. made for decades.

Today, however, it is one of the many properties that make quartz so indispensable in the modern world. Without quartz and its piezoelectric properties we would not have sonar or most modern watches and clocks; it is used in transmitting radio and TV signals; it’s even in your computer and your GPS.

We think you’ll all agree, and it’s all much more interesting and impressive than hanging up your hoo-ha.

All “explainer” articles are confirmed by fact checkers to be correct at the time of publication. Text, images and links can be edited, deleted or added at a later time to keep the information current.

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