Crystal Harvest Field Guide

Quartz: The Complete Guide

Rock crystal, the mineral inside every watch and computer, and the parent of amethyst, citrine, agate, and more. The history, science, and record-breaking crystals of the world’s best-known mineral.

Quick facts

SiO2Silicon dioxide, a 3D framework of silicon-oxygen tetrahedra. Trigonal.
7 on MohsQuartz is the reference mineral for 7 on the hardness scale.
SG 2.65RI about 1.54–1.55, birefringence 0.009.
~12% of crustSecond only to the feldspars (~41%) in the continental crust.
Left or rightQuartz crystals are either left- or right-handed, mirror images of each other.
PiezoelectricSqueeze it and it makes a voltage. Discovered by Jacques and Pierre Curie in 1880.
573 °CAt this temperature quartz switches from alpha to beta quartz, with a volume change that can crack it.
No cleavageIt breaks with a glassy, shell-shaped (conchoidal) fracture.

From “frozen ice” to your phone

Few minerals have shaped human history like quartz, from ancient ideas about ice to the oscillator that keeps time in your pocket.

  1. Ancient GreeceGreek krystallos, from kruos (“icy cold”), reflects the belief that rock crystal was ice frozen so hard it could never melt. Theophrastus held the view.
  2. 1st centuryPliny the Elder writes that crystal forms from intensely frozen snow in the Alps and notes its natural six-sided form. The ice idea persists until at least the 1600s.
  3. c. 975–996Fatimid craftsmen in Cairo carve the al-‘Aziz ewer, handle and all, from a single block of rock crystal. It is now in the Treasury of St Mark’s in Venice, one of about seven great Fatimid crystal ewers.
  4. 1500s–1600sMilan, Prague, and Florence become the great centers of carved rock crystal.
  5. 1880Jacques and Pierre Curie discover piezoelectricity in quartz.
  6. 1921–1928Walter Cady builds the first quartz crystal oscillator in 1921. Warren Marrison of Bell Labs builds the first quartz clock in 1927–28 (sources differ on the year).
  7. 1940sWorld War II radios need quartz. Brazil exports a peak of 2,411 tonnes in 1943, and the US government sets up a quartz buying station in Hot Springs, Arkansas.
  8. 1950Bell Labs has a commercial process for growing quartz in the lab. Today virtually all electronic quartz is synthetic.
  9. 1967Arkansas names quartz its official state mineral.
  10. 1969Seiko releases the Astron, the first commercial quartz wristwatch.
  11. 2008A study by the British Museum and Smithsonian shows the famous “ancient” crystal skulls were made with modern rotary tools.

How quartz forms

Quartz grows wherever silica-rich fluid has room and time. That happens in several different geological settings.

  1. Hydrothermal veins. Hot water carrying dissolved silica flows through cracks and deposits quartz as it cools. Arkansas’s crystal belt formed this way near the end of mountain building, about 280–245 million years ago.
  2. Pegmatites. Slowly cooling, fluid-rich granitic magma grows quartz crystals several meters long and hundreds of kilograms in weight.
  3. Alpine clefts. In the Alps, extension fractures opened during mountain building. Quartz grew about 22–17 million years ago at 400–450 °C, 12–14 km deep.
  4. Cavities and geodes. Silica-bearing water lines gas bubbles in lava and hollows in limestone or dolostone with crystals, as in Herkimer diamonds and amethyst geodes.
  5. Microcrystalline silica. When silica precipitates quickly or at low temperature, it forms microscopic crystals, making chalcedony, agate, chert, and flint.
  6. Weathering survivor. Quartz is so resistant that it outlasts other minerals and becomes most of the world’s sand.

The quartz family

Quartz comes in two big branches. Macrocrystalline quartz forms visible crystals. Microcrystalline quartz is made of crystals too small to see.

Rock crystal

Colorless, clear quartz.

Amethyst

Purple, from iron plus natural radiation. Amethyst guide.

Smoky

Brown to black, from aluminum plus natural radiation.

Citrine

Yellow to orange. Much of it is heat-treated amethyst.

Rose

Pink, from microscopic fibers related to dumortierite.

Milky

White, clouded by countless tiny fluid and gas inclusions.

Prasiolite

Green, usually heated amethyst.

Chalcedony family

Microcrystalline: agate (banded), carnelian, onyx, chrysoprase, bloodstone, plus jasper, chert, and flint.

Famous localities and record crystals

Quartz is everywhere, but a few places produce crystals that set the standard.

Arkansas, USA

Ouachita Mountains

A quartz belt 30–40 miles wide runs about 170 miles southwest from Little Rock. Dig-your-own sites operate around Mount Ida and Jessieville.

Brazil

Minas Gerais, Goiás, Bahia

The world’s great source of large crystals. Crystals of 1–5 tonnes occur in many deposits.

The Alps

Switzerland & Austria

Alpine cleft crystals, especially smoky quartz, collected by traditional “strahler” crystal hunters.

Herkimer, NY

Mohawk Valley

Water-clear double-terminated crystals. See our Herkimer diamond guide.

Namibia

Otjua

Home of the world’s largest crystal cluster on display.

Spruce Pine, NC

Blue Ridge

Ultra-pure quartz used to make the crucibles that grow silicon for computer chips.

Record breakers

  • Largest documented single crystal: from near Itapore, Goiás, Brazil, about 6.1 × 1.5 × 1.5 m and over 39,900 kg.
  • Largest crystal cluster on display: the Otjua cluster from Namibia (found 1985), 3 × 3 m and 14,100 kg, at the Kristall Galerie in Swakopmund. Its largest crystal is 2.2 m long and weighs about a tonne.
  • Tiefengletscher, Switzerland (1860s): about 150 tonnes of smoky quartz from one cleft, including the 133 kg “Grandfather.”
  • Planggenstock, Switzerland (2005): nearly 2 tonnes of crystals. A 300 kg cluster is on display at the Natural History Museum in Bern.

Crystal shapes and habits

Scepter

A later crystal cap grown on the tip of an older crystal.

Skeletal / window

Edges grew faster than faces during rapid changes, leaving stepped, hollow faces.

Cathedral

A main crystal with many smaller crystals grown in parallel, like spires.

Japan-law twin

Two flat crystals joined at 84°33′, forming a V or heart shape.

Double-terminated

Points on both ends, from growing free of the rock. See why.

Phantom

Ghostly outlines of earlier growth stages inside the crystal.

Rutilated

Golden to red needles of rutile trapped inside.

Enhydro

Water trapped in a sealed pocket, sometimes with a moving bubble.

Glass, lab-grown, and coated quartz

Clear quartz is easy to imitate and easy to grow. Here’s how the main look-alikes compare.

PropertyWhat it isHow to spot it
GlassAmorphous, not crystallineGlass is singly refractive, so under a polariscope it stays evenly lit as you turn it, while quartz blinks light and dark. Glass hardness varies from 4 to 7, so a scratch test isn’t reliable.
Synthetic quartzGrown on seed plates in steel autoclaves at about 400 °C and very high pressure, over roughly 80 daysCan look identical to natural quartz. Clean stones may need infrared or chemical lab testing.
Aura quartzNatural quartz coated with vaporized metal (gold, titanium, niobium, and others) in a vacuumRainbow or metallic sheen that wears off at edges. The coating is only about 1–2 microns thick and should be disclosed.
Dyed or lab-colored quartzCrackled or plain quartz with added color, or synthetic amethyst and citrineUnnatural colors and dye in cracks. See our treatment guide.

Quartz in modern technology

TimekeepingAbout 2 billion quartz oscillators were being made a year by 2003, for watches, phones, and computers.
Computer chipsQuartz is refined into silicon for semiconductors and solar panels. China made almost 80% of the world’s silicon in 2025.
CruciblesUltra-pure Spruce Pine, NC quartz makes the crucibles that grow silicon crystals for chips.
Fused silicaQuartz melted at about 2,200 °C makes glass for optics, UV lamps, and optical fiber.
Sand and glassSand that is 99%+ quartz is used for glassmaking, abrasives, foundry molds, and filler.

Myths vs. facts

Myth: Quartz is the most abundant mineral on Earth.

Fact: The feldspar group is more abundant in the continental crust (about 41% vs 12%). Quartz is the most abundant mineral in most sand.

Myth: Crystal skulls are ancient Aztec or Maya artifacts.

Fact: The museum skulls carry marks of modern rotary tools, and none come from a documented excavation. The British Museum skull is probably 19th-century European, and the Smithsonian’s was likely made in the 1950s or later.

Myth: Rock crystal is permanently frozen ice.

Fact: That was the ancient belief behind the word “crystal.” Quartz is silicon dioxide.

Myth: Crystal healing is scientifically proven.

Fact: Controlled tests found people reported the same sensations holding fake stones as real ones.

Myth: The quartz in electronics is mined.

Fact: Virtually all of it is grown in labs.

Myth: Aura quartz is a natural color.

Fact: It is a vapor-deposited metal coating.

Care and display

Cleaning

Warm soapy water and a soft brush. Avoid bleach and harsh chemicals on included or coated pieces.

Heat

Quartz can crack with sudden temperature changes. Never put a cold crystal in hot water.

Storage

At 7, quartz scratches softer stones. Store points separately so their tips don’t chip.

Sunlight

Clear quartz is stable in light, but smoky, amethyst, and rose varieties can fade over time.

Quartz in the shop

Natural Quartz Crystal Point Set — 4 Clear Points
Natural Quartz Crystal Point Set — 4 Clear Points$28.00
Double Terminated Quartz Crystal Set — 3 Natural Specimens
Double Terminated Quartz Crystal Set — 3 Natural Specimens$38.00
Hand holding a white box filled with fifteen clear quartz points of varying size
Clear Quartz Point Lot (15 Pieces)$22.96
Eight tan and amber quartz specimens from Pennsylvania laid out in two rows beside a steel caliper
Quartz Lot (8 Pieces) — Pennsylvania$27.88
Nine milky phantom quartz pieces from Merrimack County, New Hampshire laid out beside a caliper
Milky Phantom Quartz Lot (9 Pieces) — Merrimack County, New Hampshire$26.24
Hand holding a New Jersey specimen of honey calcite and quartz crystals with dark metallic sulfides
Calcite & Quartz with Sulfides — New Jersey$29.52
Eight tan and amber Pennsylvania quartz specimens arranged in two rows beside a steel caliper
Quartz Parcel — Pennsylvania$36.08
Nine milky phantom quartz pieces from Merrimack, New Hampshire arranged on white beside a caliper
Milky Phantom Quartz Parcel — Merrimack, New Hampshire$39.36
Hand holding a long slender clear quartz point with faint internal veils
Clear Quartz Crystal Point — Natural Specimen$29.52
Hand holding a milky phantom quartz cluster from New Hampshire, white crystal points packed together
Milky Phantom Quartz Cluster — New Hampshire$42.64
See all quartz

Frequently asked questions

Is clear quartz the same as crystal glassware?

No. Quartz is crystalline and doubly refractive. “Crystal” glassware is glass, which has no crystal structure.

How does quartz keep time in watches?

A quartz crystal vibrates at a steady frequency when electrified, 32,768 times per second in most watches, and the circuit counts those vibrations.

Where can I dig my own quartz?

Arkansas has fee-dig sites around Mount Ida and Jessieville, and New York’s Mohawk Valley has Herkimer diamond mines.

Can I tell natural from lab-grown quartz by eye?

Often not. Clean synthetic quartz can need lab testing to identify.

Can heat damage quartz?

Yes. Sudden temperature changes can crack it, and at 573 °C its structure changes.

What’s the biggest quartz crystal ever found?

A crystal from near Itapore, Brazil, about 6 m long and over 39 tonnes, is the largest documented.

What is quartz crystal good for?

Quartz is one of the most useful minerals on Earth. It keeps time in watches and electronics (it vibrates at a precise frequency when electrified), is the raw material for glass and high-purity silicon, is used in optics and lab equipment, and is one of the most popular minerals with collectors because of its clear, well-formed crystals.

What are the different colors of quartz?

Clear (rock crystal), milky, smoky (brown to black), amethyst (purple), citrine (yellow to orange), rose (pink), and prasiolite (green), plus blue quartz and many colors caused by inclusions, like strawberry and rutilated quartz. The microcrystalline forms, chalcedony, agate, jasper, and carnelian, come in almost every color.

What is the rarest color of quartz?

Natural green quartz (prasiolite) and deeply colored natural citrine are among the rarest, because most green and orange quartz on the market was heated. Natural blue quartz colored by tiny mineral inclusions is also uncommon.

Is quartz 100% silica?

Very nearly. Quartz is silicon dioxide (SiO2), but natural crystals contain tiny traces of other elements, measured in parts per million. Those traces (iron, aluminum, titanium, and others) are what make amethyst, smoky quartz, and citrine colored.

What minerals are mistaken for quartz?

Calcite is the most common: it is much softer (a knife scratches it), breaks into rhombs, and fizzes in dilute acid. Glass, gypsum (selenite), feldspar, and topaz are also confused with quartz. Quartz scratches glass, has no cleavage, and breaks with a curved conchoidal fracture.

How do you know if strawberry quartz is real?

Natural strawberry quartz has uneven red speckles or flakes of iron-mineral inclusions. Bright, candy-pink “cherry” or “strawberry” quartz with swirls and round bubbles is usually glass. See the most commonly faked crystals.

What makes milky quartz white?

Millions of microscopic fluid-filled bubbles trapped as the crystal grew scatter light, turning the quartz white and cloudy.

How much is a pound of quartz worth?

Common rough quartz is inexpensive and sold by the pound. Price climbs with clarity, crystal form, damage-free points, and a known locality, so a well-formed cluster or a documented specimen is worth far more than the same weight of rough. Browse our quartz specimens and lots.

Keep reading

Sources and further reading

Where sources disagree, such as the year of the first quartz clock, this page gives both.

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