Field report · 825
The complete guide to the quartz family
Amethyst, citrine, rose quartz, smoky, aventurine, agate, jasper — they're all quartz. Here's the family tree.
If you're new to gemstones, the most efficient first thing to learn is that an enormous fraction of the stones you'll encounter are some form of quartz. Quartz is silicon dioxide (SiO2) and it makes up roughly 12% of Earth's continental crust. It comes in two structural varieties — macrocrystalline (visible crystals) and cryptocrystalline (microscopic crystals) — and each variety has named subgroups.
Macrocrystalline quartz (visible crystals)
- Rock crystal — colorless transparent quartz. The base form.
- Amethyst — purple, colored by trace iron + radiation damage
- Citrine — yellow-orange, colored by iron impurities (or heat-treated amethyst)
- Smoky quartz — brown-black, colored by radiation damage to aluminum impurities
- Rose quartz — pink, colored by trace titanium / manganese / iron
- Milky quartz — translucent white, caused by microscopic fluid inclusions
- Prasiolite — green; very rare in nature, usually heat-treated amethyst
- Ametrine — natural amethyst-citrine bicolor crystals (Bolivia is the only commercial source)
- Rutilated quartz — clear quartz containing golden needle-like rutile inclusions
- Tourmalinated quartz — clear quartz with black tourmaline needles
Cryptocrystalline quartz (microscopic crystals)
Also called chalcedony as a group:
- Chalcedony — translucent, often blue-gray
- Carnelian / sard — orange to red-brown chalcedony
- Onyx — banded black-and-white chalcedony
- Agate — banded or patterned chalcedony, hundreds of subtypes (lace agate, fire agate, blue lace, etc.)
- Jasper — opaque chalcedony, often patterned (picture jasper, ocean jasper, fancy jasper)
- Bloodstone — green jasper with red iron-oxide spots
- Aventurine — translucent quartz with mica or fuchsite inclusions giving sparkle
- Tiger eye — silica replacement of crocidolite, giving fibrous gold/brown chatoyancy
- Chrysoprase — green chalcedony colored by nickel
What this means for buyers
The quartz family covers a huge price range — from $2/lb tumbled aventurine to $5,000+ for top Russian demantoid... wait, that's andradite, not quartz. Within the quartz family alone: $2 for aventurine tumbles to $3,000+ for top Uruguayan amethyst geodes. The shared chemistry means similar care (Mohs 7, durable for daily wear, not acid-sensitive) and similar treatments (irradiation, heat).
If you're starting a collection, learning to recognize the quartz family first will dramatically speed up your education on every other stone you encounter.