Quick answer: among natural colors, the rarest quartz is natural green quartz (prasiolite), which Wikipedia’s mineral entry calls “exceedingly rare,” along with transparent pink quartz crystals and true blue quartz. Most green quartz on the market is heated amethyst, and most bright blue “quartz” is treated “aqua aura.” Clear, milky, and smoky quartz are the most common colors.
Why quartz has colors at all
Pure quartz is colorless. Every color comes from something extra: a few parts per million of a trace element sitting in the crystal lattice, natural radiation that changes how those atoms hold electrons, or microscopic inclusions of another mineral. Amethyst, for example, owes its purple to roughly 10–100 parts per million of iron activated by natural radiation, according to UT Austin’s EarthDate. (The chemistry behind all of this is in Trace Elements: The Impurities That Actually Give Crystals Their Color.)
Quartz colors, roughly from common to rare
Common: clear, milky, and smoky
Clear rock crystal and milky quartz (white from countless tiny fluid inclusions) are everywhere. Smoky quartz, colored by natural radiation acting on aluminum in the lattice, is also widespread; see our Double Terminated Smoky Quartz Point and the story in Smoky Quartz: A Color Built by Radiation, Not Dye.
Common, but valued: amethyst
Purple quartz is mined in volume in Brazil and Zambia, with notable sources in Bolivia and Arizona (GIA). Deep, even color is what is uncommon. Our Brandberg Amethyst Crystal Cluster — Tafelkop, Namibia from Namibia shows the darker end.
Less common: natural citrine
Yellow to orange quartz that formed that way in the ground is far scarcer than the citrine in most shops, which is usually heat-treated amethyst. GIA notes that some amethyst turns yellow when heated. (Full story: Citrine: Why Most of It Started Out as Amethyst.)
Uncommon: rose quartz, especially as crystals
Massive rose quartz is common, but it almost never forms crystals. Wikipedia’s rose quartz entry explains that massive rose quartz is colored by microscopic fibers related to dumortierite and is “always anhedral,” without crystal faces. True transparent pink quartz crystals are a different material, colored by aluminum and phosphorus color centers, forming late in pegmatite pockets, and they are photosensitive and can fade. Those crystals are a genuine collector rarity.
Rare: blue quartz
Minerals.net describes natural blue quartz as a rare variety colored by inclusions of blue minerals, especially dumortierite, with a duller gray-blue form colored by crocidolite fibers. Most bright sky-blue “quartz” for sale is “aqua aura”: colorless quartz coated with gold in a treatment process. Transparent, naturally sky-blue quartz crystals essentially do not occur.
Rarest: natural green quartz (prasiolite)
Natural prasiolite was first found in Lower Silesia, Poland, in the early 1800s, and only a handful of other deposits are known (including Thunder Bay, Canada, and Rooisand, Namibia). Nearly all green quartz sold today is manufactured: in the mid-1950s it was discovered that amethyst from the Montezuma mine in Minas Gerais, Brazil, turns green when heated to about 400–500 °C, according to Wikipedia’s prasiolite entry. If someone offers natural green quartz cheaply, it is almost certainly heated amethyst.
A note on “rare” vs “expensive”
Rarity does not map neatly onto price. Fine deep amethyst can outsell rare-but-pale natural colors because the market knows and wants it. For collectors, what matters is whether the color is natural and whether the seller says so.
Color can change
Several quartz colors are not permanent. Amethyst and pink quartz can fade in strong light, and heat can turn amethyst yellow or green. If you own colored quartz, keep it out of sunny windows. See Why Amethyst Fades in Sunlight.
Quick FAQ
Is green quartz natural?
Rarely. Natural prasiolite exists but is exceedingly rare; most green quartz is amethyst that was heat-treated to turn green.
Is blue quartz real?
Natural blue quartz exists but is rare and colored by mineral inclusions. Most bright blue quartz on the market is ‘aqua aura,’ clear quartz treated with gold.
What is the most common quartz color?
Colorless (rock crystal) and milky white, followed by smoky brown.
Sources
- Wikipedia: Prasiolite
- Wikipedia: Rose quartz
- Minerals.net: Blue Quartz
- GIA: February Birthstone — Amethyst
- EarthDate (UT Austin Bureau of Economic Geology): Amethyst
