Quartz
A hard, abundant mineral used in jewelry and technology.
Quartz is a hard mineral composed of silica, or silicon dioxide, with its atoms arranged in a continuous framework of SiO₄ tetrahedra, where each oxygen atom is shared between two tetrahedra, giving it the chemical formula SiO₂. Structurally, it is classified as a framework silicate, and compositionally as an oxide mineral. It is the second most common mineral in Earth’s lithosphere, accounting for roughly 12% of its mass. Quartz defines the value of 7 on the Mohs scale of hardness. The mineral exists in two forms: normal α-quartz and high-temperature β-quartz, both of which are chiral. The transformation from α- to β-quartz occurs abruptly at a specific temperature, accompanied by a significant volume change that can induce microfracturing in ceramics, ornamental stone after a fire, or rocks exposed to high heat. α-quartz crystallizes in the trigonal system, while β-quartz has greater symmetry and crystallizes in the hexagonal system; β-quartz is unstable at room temperature, so all quartz at ordinary conditions is α-quartz. The ideal crystal shape is a six-sided prism with six-sided pyramid-like rhombohedrons at each end, though natural crystals are often twinned, distorted, or intergrown. Well-formed crystals commonly occur as a druse lining a void, as in quartz geodes. The word “quartz” derives from the German word, which came from a Polish dialect term meaning “hard.” The Ancient Greeks called it “crystal,” meaning “icy cold,” believing it to be supercooled ice, an idea that persisted through Roman naturalist Pliny the Elder and into the 17th century. In that century, Nicolas Steno’s study of quartz established the law of constancy of interfacial angles, paving the way for modern crystallography. Pure quartz is colorless and transparent, known as rock crystal. Colored varieties—such as amethyst, citrine, rose quartz, smoky quartz, and milky quartz—arise from impurities that alter molecular orbitals, causing electronic transitions in the visible spectrum.
- chemical_formula
- SiO2
- classification
- Framework silicate mineral and oxide mineral
- hardness
- 7 on Mohs scale
- crystal_system
- Trigonal (α-quartz) and hexagonal (β-quartz)
- common_varieties
- Rock crystal, amethyst, citrine, rose quartz, smoky quartz, milky quartz
Lore & Background
Quartz is a hard mineral composed of silica, with its atoms arranged in a continuous framework of silicon-oxygen tetrahedra, each oxygen shared between two tetrahedra, giving it the chemical formula SiO₂. It is structurally a framework silicate and compositionally an oxide mineral, and it is the second most common mineral in Earth’s lithosphere, making up about 12% of its mass. Quartz exists in two forms: normal α-quartz and high-temperature β-quartz, both of which are chiral. The transformation from α- to β-quartz occurs abruptly at a specific temperature and is accompanied by a significant volume change, which can cause microfracturing in ceramics or rocks that pass through this temperature threshold. Quartz defines the value of 7 on the Mohs scale of hardness. Its ideal crystal shape is a six-sided prism with six-sided pyramid-like rhombohedrons at each end, though natural crystals are often twinned, distorted, or intergrown. Well-formed crystals typically appear as a druse lining a void, such as in quartz geodes, with crystals attached at one end; doubly terminated crystals occur when they develop freely, as within gypsum. Pure quartz, known as rock crystal, is colorless and transparent, while colored varieties like amethyst, citrine, rose quartz, smoky quartz, and milky quartz arise from impurities that alter molecular orbitals, causing visible light absorption. Varieties are classified by crystal visibility: macrocrystalline (visible to the eye), microcrystalline (visible only under a microscope), and cryptocrystalline (too small for an optical microscope).
Reader's Guide
Quartz is a hard, framework silicate mineral composed of silicon dioxide, with its atoms arranged in a continuous network of linked tetrahedra. It is the second most common mineral in Earth’s lithosphere, making up about 12% of its mass. Quartz exists in two chiral polymorphs: α-quartz, which is stable at room temperature and crystallizes in the trigonal system, and β-quartz, which forms at higher temperatures in the hexagonal system. The transition between them occurs abruptly at a specific temperature and is accompanied by a significant volume change, which can cause microfracturing in ceramics, ornamental stone, or rocks exposed to high heat. The mineral defines hardness 7 on the Mohs scale. Its varieties have been used in jewelry and hardstone carvings since antiquity, especially in Europe and Asia. The word “quartz” likely derives from a German term, itself from a Polish or Czech word meaning “hard.” Ancient Greeks called it “crystal,” believing it to be supercooled ice, a view held by Pliny the Elder and persisting into the 17th century. In the 17th century, Nicolas Steno’s study of quartz crystals established the law of constancy of interfacial angles, laying groundwork for modern crystallography. Quartz crystals ideally form six-sided prisms with pyramidal ends, though twinning, distortion, or intergrowth with other minerals is common. Well-formed crystals often line voids as druses, with quartz geodes being notable examples. Pure quartz is colorless and transparent, while impurities produce colored varieties such as amethyst, citrine, rose quartz, smoky quartz, and milky quartz.
Did You Know?
- Quartz is the second most common mineral in Earth's lithosphere, comprising about 12% by mass.
Common Misconceptions (Editorial)
Some people think quartz is rare or only found as clear crystals, but it is actually the second most common mineral in Earth’s lithosphere, comprising about 12% by mass. Others believe the ancient idea that quartz is permanently frozen ice, but this is a misconception—quartz is a hard mineral composed of silica (silicon dioxide), not ice.
Why It Matters (Editorial)
Quartz endures as a subject of fascination not only for its beauty in jewelry and carvings but also for its pivotal role in the history of science. The 17th-century studies of quartz by Nicolas Steno established the law of constancy of interfacial angles, laying the groundwork for modern crystallography, which remains fundamental to geology, chemistry, and materials science.
More in Gemstones 1-22
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record