Quartz — a mineral found everywhere that still manages to surprise
Quartz — Earth's "extrovert": abundant, adaptable, and always ready to shine beautifully. It grows in transparent rock crystal prisms, violet amethyst, smoky shades, sunny citrine, gentle rose quartz, and the entire microcrystalline chalcedony family — agates and jaspers. Its hardness is Mohs 7, it polishes excellently and — due to piezoelectricity — precisely keeps time in your watch. If minerals had CVs, quartz's would say "I do everything well" and be attached with a thousand photos.
Identity and "family tree" 🔎
Macro vs. micro (chalcedony)
Macrocrystalline quartz forms visible crystals: rock crystal, amethyst, citrine, smoky, rose, milky. Micro/cryptocrystalline quartz is chalcedony (fibrous micro-quartz + moganite), which forms agate (banded), jasper (opaque), flint/chert, carnelian, chrysoprase, and more.
Polymorphic "relatives"
Same chemistry, different structures: high-temperature tridymite and cristobalite; high-pressure coesite and stishovite. Quartz — the Earth's surface "low-pressure" champion.
Where quartz grows 🧭
Hydrothermal veins and geodes
Silicon-rich solutions cool in cracks and cavities, lining them with prismatic crystals. In volcanic regions, gas bubbles turn into geodes — with amethyst "cathedrals" and shiny druses.
Pegmatites
Late phases of granitic melts grow large-space crystals. Quartz faithfully accompanies feldspar, tourmaline, beryl, and others.
Sedimentary and metamorphic environments
Quartz cement binds sandstones; in metamorphism, sand "baked" turns into quartzites. Microquartz replaces fossils and wood with astonishing precision.
Colors — according to physics and chemistry
Amethyst (Fe color centers + radiation); smoky (Al centers + irradiation); citrine (heated amethyst or Fe centers); pink (microscopic fibrous inclusion phases — often similar to dumortierite); milky (fluid microinclusions).
Worth knowing inclusions
Rutile "golden needles", tourmaline rods (schorl), chlorite "gardens", phantoms (pale growth outlines), and rare enhydros (liquid bubbles).
Artificial, but excellent
Hydrothermal lab quartz is grown for optics and electronics — chemically identical crystals grown on seed plates, perfectly clean.
In short: if water can bring dissolved silicon there, quartz can come and "decorate" the space.
Color and pattern glossary 🎨
Palette
- Rock crystal — colorless, transparent.
- Amethyst — from lilac to deep violet.
- Citrine — from pale yellow to honey.
- Smoky — from tea color to almost black ("morion").
- Pink — softly pink, often milky.
- Milky — opaline whiteness due to microbubbles.
Chalcedony adds banded agate, opaque jasper, orange-toned carnelian, apple-green chrysoprase, and more.
Growth form terms
- Prismatic hexagonal crystals with pyramids at the ends; common Dauphiné and Brazilian twinning.
- "Japan‑law" twins — two crystals in a V shape at ~84.6° angle (collector favorites).
- Druses (fine crystal coating); scepters (late "crown" on an earlier "stem"); skeletal and "window" growth in rapidly cooling cavities.
Photography tip: Backlight thin edges to make the color "ring"; ~30° side lighting emphasizes planes and striations. A black card behind a clear crystal gives a sharp silhouette.
Physical and optical properties 🧪
| Property | Typical range / Note |
|---|---|
| Chemistry | SiO₂ (silicon dioxide) |
| System | Trigonal (α-quartz under normal conditions) |
| Hardness | ~7 on Mohs scale (scratches glass; resistant to everyday wear) |
| Relative density | ~2.65 |
| Cleavage / Fracture | No true cleavage; conchoidal fracture with “shell” waves |
| Refractive index | ~1.544–1.553; double refraction ~0.009; uniaxial (+) |
| Optical effects | “Rainbows” from healed microfractures; aventurescence in aventurine (fuchsite/getite plates) |
| Electrical properties | Piezoelectric (mechanical stress ↔ electric charge), basis of timers and oscillators |
Under the loupe / collector's hints 🔬
Faces and striations
Main prism faces show weak horizontal striations. Tip symmetry can reveal left-/right-handed crystals; twins often have repeating, mirror-image growth steps.
Color zoning and phantoms
Amethysts often show zoning towards the tips; phantoms (ghostly outlines) mark growth pauses — each like a timestamp in the crystal's biography.
Inclusion stories
Rutile needles cross like golden straws (rutile quartz); black tourmaline (schorl) rods create graphic patterns; chlorite “gardens” add greenery; tiny fluid inclusions move like living things when warmed.
Similar minerals and how to distinguish 🕵️
Glass
Amorphous, lacks crystal planes; bubbles often spherical and uniform in size; RI ~1.50 (lower). Quartz has natural planes/striations and greater hardness (7 vs. ~5.5).
Calcite
Softer (3), has perfect cleavage and distinct double refraction; reacts with acid. Quartz has no cleavage and does not fizz.
Feldspar and topaz
Feldspars have two cleavage directions ~90°, often cloudy; topaz is harder (8) with basal cleavage. Cleavage — a quick hint: quartz does not have it.
Dyed agate vs. natural
Neon, uniform banded chalcedony shades indicate dyeing; in natural agate bands are subtly, unevenly toned, transitions gradual.
Synthetic quartz
Hydrothermal growth can be very clean with "chevron" zoning and seed plate traces; natural stones more often have microbubbles, mineral inclusions, or uneven zoning.
Quick checklist
- Hardness 7; no cleavage; vitreous luster.
- Crystal planes/striations for macrotopes.
- In agates — banding and semi-transparency; in jasper — opacity.
Localities and famous forms 📍
Crystal classics
Brazil (Minas Gerais) — large, fine crystals and amethyst; Arkansas, USA — crystal-clear deposits; Alps — smoky quartz and gwindel (twisted crystals); Herkimer County, New York — "Herkimer diamonds" (doubly terminated in dolomite cavities).
The world of chalcedony
Uruguay and Brazil — amethyst geodes; Madagascar — banded agates and jaspers; US Pacific Northwest — famous "landscape" jaspers; worldwide — agate "fortification" patterns in numerous nodules.
Care and display 🧼
Everyday behavior
- Quartz is hard, but sharp impacts can chip peaks/edges.
- Keep separate from softer stones (quartz usually "wins" scratching battles).
- Avoid sudden thermal shock (very hot → very cold).
Cleaning
- Running water + mild soap + soft brush; rinse well, dry with microfiber.
- Avoid bleach and strong acids — they don't help and can affect inclusions or the matrix.
- Ultrasound: generally suitable for clean crystals, but avoid heavily included/filled stones.
Display ideas
- Backlight geode slices so the bands "shine"; apply side light to tips so the planes sparkle.
- A pair: one transparent crystal + one rutile + one banded agate — one species, three characters.
Practical tests 🔍
Hardness reality test
On a spare glass tile, the quartz edge will leave a line (hardness 7). Do not use your window — quartz enthusiastically proves what it can do.
Phantom hunting
A rock crystal under a bright point light often reveals phantom outlines. Slowly tilt and look for pale triangular pyramids at the crystal's tip.
A little joke: quartz is that friend who comes to help when moving, keeps perfect time, and also brings sparkle. Reliable and wonderful.
Questions ❓
Is all citrine natural?
Not necessarily. Much on the market is heat-treated amethyst (a deeper orange, often with white bases). Natural citrine is usually paler and more uniform.
Why are some pink quartzes cloudy?
Microscopic fibrous inclusion phases scatter light, giving a soft, milky appearance. Faceted "transparent" pink quartz is rarer.
What is the difference between quartz and quartzite?
Quartz is a mineral. Quartzite is a metamorphic rock made of fused quartz grains. Quartzite easily scratches steel and shows a "sugary" granular texture on fresh breaks.
Are "Herkimer diamonds" diamonds?
No — these are simply wonderfully clear, doubly terminated quartz crystals from dolomite cavities. They sparkle as if trying to get on stage — hence the nickname.
Why do some transparent crystals show small rainbows?
Small internal cracks or fluid films act like prisms, dispersing light into interference rainbows when the angle is "right."