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—responsible for agate (banded), jasper (opaque), chert/flint, carnelian, chrysoprase, and more.

Polymorph cousins

Same chemistry, different structures: high‑temperature tridymite and cristobalite; high‑pressure coesite and stishovite. Quartz is the low‑pressure champion at Earth’s surface.

Hydrothermal veins & geodes

Silica‑rich fluids cool in cracks and cavities, lining them with prismatic crystals. In volcanic terrains, gas bubbles become geodes—amethyst cathedrals and sparkling druses included.

Pegmatites

Granitic late‑stage melts grow large crystals with room to stretch. Quartz is the faithful backdrop to feldspar, tourmaline, beryl, and friends.

Sedimentary & metamorphic

Quartz cement binds sandstones; pressure cooks sand into quartzite in metamorphism. Microcrystalline quartz replaces fossils and wood in exquisite detail.

Colors by physics & chemistry

Amethyst (Fe color centers + radiation); smoky (Al centers + irradiation); citrine (heated amethyst or Fe centers); rose (microscopic fibrous inclusions—often dumortierite‑like); milky (fluid inclusions).

Inclusions worth knowing

Rutilated quartz (gold needles), tourmalinated quartz (black tourmaline), chlorite “gardens”, phantoms (faint growth outlines), and rare enhydros (fluid bubbles).

Artificial but awesome

Hydrothermal lab‑grown quartz is produced for optics and electronics—chemically identical, grown on seed plates, and impeccably clear.

Palette

• Rock crystal — colorless, transparent.
• Amethyst — lilac to royal violet.
• Citrine — pale lemon to honey.
• Smoky — tea to near‑black (“morion”).
• Rose — soft pink, often milky.
• Milky — opalescent white from micro‑bubbles.

Chalcedony adds banded agate, opaque jasper, carnelian oranges, apple‑green chrysoprase, and more.

Habit words

• Prismatic hexagonal crystals ending in pyramids; common Dauphiné & Brazil twinning.
• Japan‑law twins — two crystals in a V at ~84.6° (collector favorites).
• Drusy coatings of tiny crystals; scepters (a late crown over an earlier stalk); skeletal and window growth in fast‑cool cavities.

Photo tip: Back‑light thin edges to make color hum; side‑light ~30° for faces and striations. A black card behind clear crystal produces crisp silhouettes.

Faces & striations

Primary prism faces show faint horizontal striations. Termination symmetry can reveal left/right‑handed crystals; twins may show repeated, mirror‑like growth steps.

Color zoning & phantoms

Amethyst often displays zoned color toward terminations; phantoms (ghostly outlines) mark pauses in growth—each a time stamp in crystal biography.

Inclusion stories

Rutile needles cross like golden straw (rutilated quartz); black tourmaline rods (schorl) make bold graphics; chlorite gardens tint green; tiny fluid inclusions shimmer with movement when warmed.

Glass

Amorphous, lacks crystal faces; bubbles may be spherical and evenly sized; RI ~1.50 (lower). Quartz shows natural faces/striations and higher hardness (7 vs. ~5.5).

Calcite

Softer (3), shows perfect cleavage and strong double refraction; reacts with acid. Quartz has no cleavage and does not fizz.

Feldspar & topaz

Feldspar has two cleavages at ~90°, often cloudy; topaz is harder (8) with basal cleavage. Cleavage is the quick tell—quartz doesn’t have it.

Dyed agate vs. natural

Neon, uniform color in banded chalcedony suggests dye; natural agate shows subtle, uneven band tones and gradual transitions.

Synthetic quartz

Hydrothermal growth can be ultra‑clean with chevron zoning and seed‑plate evidence; natural stones often include micro‑bubbles, mineral inclusions, or uneven zoning.

Quick checklist

• Hardness 7; no cleavage; vitreous luster.
• Crystal faces/striations in macro types.
• Banding & translucency in agate; opacity in jasper.

Crystal classics

Brazil (Minas Gerais) — large, fine crystals and amethyst; Arkansas, USA — water‑clear clusters; Alpine region — smoky quartz & gwindels (twisted crystals); Herkimer County, NY — “Herkimer diamonds” (doubly terminated in dolostone).

Chalcedony world

Uruguay & Brazil — amethyst geodes; Madagascar — banded agates and jaspers; Pacific Northwest, USA — celebrated picture jaspers; Worldwide — agate nodules & fortification patterns galore.

Everyday handling

• Quartz is tough, but sharp impacts can chip tips/edges.
• Store separately from softer stones (quartz wins most scratch fights).
• Avoid sudden thermal shock (very hot → very cold).

Cleaning

• Lukewarm water + mild soap + soft brush; rinse well, dry with microfiber.
• Skip bleach and strong acids; they don’t help and may attack inclusions/matrix.
• Ultrasonic: usually fine for clean crystals, but avoid for included/filled stones.

Display ideas

• Back‑light geode slices to make bands glow; side‑light points for face sparkle.
• Pair a clear crystal with a rutilated and a banded agate—one species, three personalities.

Hardness reality check

On a spare glass tile, a quartz edge will leave a line (hardness 7). Do not use your window—quartz is enthusiastic about proving its point.

Phantom hunt

Rock crystal under a bright point light often reveals phantom outlines. Tilt slowly and look for faint triangular pyramids inside the main termination.