48 Fun Facts About Quartz

The sarsens, the huge blocks of which ancient monument, are a rock made almost entirely of quartz?

Stonehenge. A core drilled from one sarsen during repairs in 1958 was kept as a souvenir for sixty years; once handed back, it showed grains of quartz cemented together by yet more quartz.

Quartz defines 7 on the Mohs scale; which gem mineral defines 8?

Topaz. Friedrich Mohs picked ten minerals in 1812 so that each one scratches all those below it, so quartz will mark the six softer minerals on his list but is itself scratched by topaz.

Milky quartz owes its cloudy white colour to what trapped inside the crystal?

Tiny bubbles of fluid. Milky quartz is very common, yet the gas and liquid sealed inside it as it grew leave it too cloudy to be wanted as a gemstone.

The Ancient Greeks called clear quartz krystallos because they believed it was a permanent form of what?

Ice. They took clear quartz for water frozen so deeply it would never thaw, and the idea is fossilised in our word 'crystal', from krystallos, which meant ice as well as the stone.

The word quartz is thought to come from an old Slavic word meaning what?

Hard, as in Czech tvrdý and Polish twardy. That is the favoured theory, though not the only one: a rival account traces the name to an old Saxon word for cross-vein ore.

The first practical use of quartz's piezoelectric effect, in the First World War, was a device built to detect what?

Submarines. The French physicist Paul Langevin sandwiched thin quartz crystals between steel plates to send out pulses of ultrasound and listen for the echo.

Quartz abruptly changes its crystal structure and volume at 573 °C, a notorious hazard in which craft?

Pottery. Clay is full of quartz grains, so ware heated or cooled too quickly through that point can crack as the grains suddenly swell or shrink, a fault potters call dunting.

A quartz crystal's prism has as many sides as which of these?

Honeycomb cell: six. Most crystals show a point at one end only, because they grew outward from a rock wall; the rare ones that grew unattached are pointed at both ends.

Kitchen worktops sold as 'quartz' are slabs of crushed quartz bound together with what?

Resin. The slabs are roughly nine-tenths ground quartz and one-tenth polymer glue, pressed and cured in a factory, which is why the trade's own name for them is engineered stone.

Which brothers discovered the piezoelectric properties of quartz in 1880?

The Curies. Pierre was 21 and working with his older brother Jacques, years before he met Marie, and a quartz instrument the brothers built went on to help her measure radioactivity.

The word piezoelectricity means electricity resulting from what?

Pressure. Squeeze a quartz crystal and a voltage appears across it, and the trick runs backwards too: apply a voltage and the crystal flexes, the steady twitch that keeps a quartz watch on time.

The first quartz clock was built in 1927 by the engineer Warren Marrison at which laboratory?

Bell Telephone Laboratories. Marrison was not trying to tell the time at all: he was after a steadier electrical frequency standard, and the clock fell out of counting a crystal's vibrations.

The quartz crystal in most watches, oscillating 32,768 times a second, is cut in the shape of a tiny what?

Tuning fork. The odd-looking number is 2 to the power of 15, so a chip need only halve the count 15 times over to arrive at one tick a second.

The world's first commercial quartz wristwatch, the Astron of December 1969, was made by which company?

Seiko. Quartz watches soon grew cheap and plentiful, and the flood of them dealt Switzerland's mechanical watchmakers the blow remembered as the quartz crisis.

Slices of quartz crystal were first widely used to stop which stations drifting off their frequencies?

Radio. In the 1920s stations wandered off their assigned frequencies and interfered with their neighbours; a slice of quartz, which keeps to one fixed rate, locked each transmitter in place.

The Second World War's demand for quartz crystals pushed industry to start doing what?

Growing them. Mines could not keep up, so engineers learned to grow quartz from superheated, silica-rich water, much as nature does, and today most electronic quartz is made that way.

The Spruce Pine Mining District, a major source of ultra-pure quartz for silicon wafers, is in which US state?

North Carolina. This one Appalachian district is among the few places on Earth with quartz pure enough for chip-making, so when a hurricane flooded it in 2024 the mines stopped and chip-makers faced the threat of a shortage.

Quartz is one of the main minerals in which speckled rock, widely used for kerbstones, monuments and worktops?

Granite. Its glassy grey grains are quartz, and you can pick them out by eye because the molten rock cooled slowly deep underground, giving every crystal time to grow large.

Amethyst takes its name from Greek words meaning what?

Not intoxicated. The Greeks linked the wine-coloured stone with Dionysus and believed it kept a drinker sober; centuries later bishops took to wearing it in their rings.

Amethyst ranked with diamond and ruby as a 'cardinal gem' until huge deposits found in which country made it plentiful?

Brazil. Until then fine amethyst came from only a few places, such as Russia's Urals; afterwards a gem once as rare as ruby became one almost anyone could afford.

Most commercially sold citrine, the yellow gem, is actually produced how?

Heating amethyst or smoky quartz. Natural citrine is rare, so most of what the shops sell began as another colour of quartz and was baked until it turned yellow or orange.

The two-tone purple and yellow quartz called ametrine is mined almost entirely in which country?

Bolivia. Nearly all of it comes from one remote mine in the east of the country; legend has it a Spanish conquistador found the deposit in the 1600s, after which it lay forgotten for three centuries.

Heliotrope, a dark green quartz gemstone flecked with red, is better known by which name?

Bloodstone. The red flecks owe their colour to haematite, a mineral whose own name comes from the Greek for blood, so the stone is named for blood twice over.

Smoky quartz gets its brown-to-black colour from what acting on it underground?

Natural radiation. Rays from the surrounding rock work on traces of aluminium in the crystal, and clear quartz can be turned smoky the same way in a laboratory.

Cairngorm quartz, a smoky variety, is named after mountains in which country?

Scotland. Nineteenth-century fashion for Highland jewellery soon outran what the mountains could supply, so many of the stones sold as cairngorms had never been near them.

Layered onyx, a pale band over a dark one, was the classic stone for which jewellery?

Cameos. The carver cut the figure from the pale upper band and cleared the rest away to bare the dark band beneath, so that a pale figure stands out against a dark ground.

The microcrystalline forms of quartz, such as carnelian and onyx, are grouped together under what name?

Chalcedony. Its crystals are so fine they show only under a microscope, and the stone is porous enough to drink up dye, which is how many of the vividly coloured slices in gift shops got their colour.

Ancient writers said which banded gem was named after the Achates, a river in Sicily?

Agate. Theophrastus and Pliny both told the story, though word historians point out that the river could just as easily have been named after the stone.

Onyx comes from the Greek for which body part, which its pink-and-white bands resemble?

Fingernail. The name was coined for pink-and-white banded stones, a long way from the solid black most people picture, and English 'nail' is a distant cousin of the same Greek word.

Chatoyancy, a gliding band of light on polished stone, marks which golden-brown quartz gem?

Tiger's eye. Fine parallel fibres run through the quartz, and light glancing off them makes the moving stripe, also called a cat's-eye.

The common red colour of jasper is due to inclusions of what?

Iron. The element that reddens rust and bricks does the same to jasper, a quartz so loaded with foreign matter that, unlike most of its cousins, it lets no light through at all.

Flint, a form of chert prized for Stone Age tools, typically occurs as nodules in which rock?

Chalk. Struck against steel, a flint throws sparks hot enough to light tinder or gunpowder, which is how the flintlock musket got its name.

Aventurine, a quartz that glitters with tiny flakes of mica, has a name that comes from a word meaning what?

By chance. The name first belonged to a spangled glass, born in one story when a Murano workman let copper filings fall into the melt, and only later passed to the stone that looked like it.

Herkimer diamonds, prized double-terminated quartz crystals, are found in dolomite in which US state?

New York. They take their name from Herkimer County, and they are not diamonds at all: the crystals come to a point at both ends because they grew with almost no contact with the rock around them.

British Museum research showed its 'Aztec' crystal skull was carved with what, proving a 19th-century origin?

Rotary jeweller's tools. Aztec carvers worked stone with hand tools and abrasive sand, so the neat wheel-cut lines gave the game away, and the skull's trail leads back to a Paris antiquities dealer, Eugène Boban.

The Mitchell-Hedges crystal skull was allegedly found in 1924 at Lubaantun, in what is now which country?

Belize. The jungle-temple story does not survive the paper trail: Mitchell-Hedges bought the skull at a Sotheby's auction in London in 1943.

'Shocked' quartz grains found worldwide in rock 66 million years old are key evidence for what?

Giant asteroid impact. A volcanic eruption cannot squeeze quartz with enough force to leave these microscopic scars, so grains lying at the very level where the dinosaurs vanish point to a blow from space.

Coesite, a form of silica made only by immense crushing force, was first found in nature in 1960 at which Arizona site?

Barringer Crater. The mineral was known from the laboratory first: the chemist Loring Coes had made it only seven years earlier, and here it was lying in the Arizona desert.

Fulgurites, hollow tubes of the natural silica glass lechatelierite, form when quartz sand is hit by what?

Lightning. A strike melts the sand along its path in an instant, leaving a rough glass tube that traces the bolt's route into the ground, which is why fulgurites are nicknamed fossilised lightning.

Quartz clocks were the world's most accurate timekeepers until they were overtaken in the 1950s by clocks based on what?

Vibrating atoms. No two quartz crystals are ever quite alike, but every caesium atom keeps exactly the same beat, which is why the second itself has been defined by caesium since 1967.

Quartzite, one of the toughest of all rocks, forms when which rock is heated and squeezed deep underground?

Sandstone. Heat and burial weld its quartz grains into one interlocking mass, so the new rock no longer breaks around the grains, as sandstone does, but straight through them.

In a British test of crystal healing, volunteers meditating with fake crystals reported what, compared with those holding real quartz?

Just the same sensations. The feelings people expected from a crystal turned up whether the stone was real or fake, which is why the researchers put crystal healing down to the placebo effect.

Breathing fine crystalline silica dust from cutting quartz-bearing stone can cause which lung disease?

Respirable crystalline silica is a recognised human carcinogen as well.

Which mineral group is the only one more abundant than quartz in the Earth's lithosphere?

Feldspar. It is a whole family of minerals, and counted together they outweigh everything else in the crust; but where quartz survives the weather to become sand, feldspar rots away into clay.

In 1992 a hollow quartz skull bigger than a human head arrived anonymously by post at which museum?

The Smithsonian. An unsigned note called the 30-pound skull Aztec, but the museum's own investigation concluded that it had been made in modern times.

Fused quartz, made by melting pure quartz, barely swells when heated, which makes it ideal for the mirrors and lenses of what?

Telescopes. A precision mirror must hold its shape as the temperature changes, and fused quartz hardly moves; it also lets through ultraviolet light, which ordinary window panes block.

What is the name for a dull, rounded rock that splits open to reveal a hollow lined with quartz crystals?

A geode. Mineral-rich water seeps into a gas bubble or other hollow in the rock and, over a very long time, grows crystals inward from the walls; a carpet of small crystals like this is called a druse.

In fracking, rounded grains of quartz sand are pumped down oil and gas wells to do what?

Prop open the cracks. Pumped water splits the rock, and the sand grains, which resist crushing, wedge in the fractures so that oil and gas can keep flowing once the pumps stop.