Quick answer: anywhere from minutes to about a million years, depending on the mineral and how supersaturated its fluid is. Bismuth hopper crystals grow in minutes as molten metal cools. Lab-grown quartz in industrial autoclaves takes weeks to months. Cave formations add fractions of a millimeter per year. And the record for slowest measured growth belongs to the giant gypsum crystals of Mexico’s Naica mine: about a billionth of a meter per day.
The slowest crystal growth ever measured
In 2011, a Spanish and Japanese team published in PNAS what they called the slowest directly measured normal growth rate for any crystal growth process: about 1.4 × 10-5 nanometers per second at 55 °C (phys.org). They recreated the Naica cave’s mineral water in the lab and measured the growth of gypsum faces with a white-beam phase-shift interferometry microscope, an instrument able to detect changes on a molecular scale.
The consequence: Naica’s crystals, up to 11 meters long and about a meter thick, needed on the order of a million years to grow. A 1 m-thick crystal would take about 990,000 years at 55 °C, but only about 500,000 years at 56 °C. A single degree halves the time. Growth only happened in a narrow window below 58 °C, the temperature where gypsum gives way to anhydrite; at 50 °C they saw no growth at all (phys.org, PNAS 2011).
The cave sat flooded at that narrow temperature range until mine pumps lowered the water table. Miners broke into it in April 2000, and it was allowed to reflood in October 2015 when mining stopped (Wikipedia). More in The Cave of Crystals.
Why speed changes everything
The rule of thumb: slow growth makes few, large, clean crystals; fast growth makes many small or skeletal ones. When a fluid is only barely oversaturated, new crystals rarely start (nucleate), so the material that does come out of solution piles onto the crystals already there. When a fluid is wildly oversaturated, crystals start everywhere at once and grow in branching or hollow shapes. That is why fast-cooled bismuth makes hollow “hopper” staircases (the edges grow faster than the face centers can fill in) and why druzy crusts are made of thousands of tiny points. See Nucleation.
A timeline of crystal growth speeds
- Seconds to minutes: bismuth crystals forming as a melt cools; snowflakes; salt crusts on a drying puddle.
- Days to weeks: kitchen-borax and alum crystals; synthetic quartz in a hydrothermal autoclave, where seed plates thicken under high temperature and pressure for weeks to months before harvest. Every quartz watch oscillator starts this way.
- Years to centuries: stalactites and other cave formations, which often add only fractions of a millimeter a year. See How a stalactite actually grows.
- Thousands to millions of years: large natural quartz, amethyst, and pegmatite crystals growing from slow-cooling hydrothermal fluids, and the record-slow Naica gypsum.
Can you tell how fast a crystal grew by looking at it?
Sometimes. Phantoms inside quartz record pauses in growth, when dust or another mineral settled on the faces before growth resumed (see Phantom quartz). Color zoning in amethyst records changing fluid chemistry. Skeletal or hollow shapes record fast growth. Perfectly flat, glassy faces, like those on Herkimer diamonds, point to slow, steady growth in a quiet cavity.
FAQ
Do crystals keep growing after they’re mined? No. A crystal needs to sit in a saturated fluid to grow. On a shelf it is finished.
How long did a Herkimer diamond take? Nobody has measured an exact rate, but they grew in cavities of 500-million-year-old dolostone from slow mineral fluids, with no time pressure at all. See The Mohawk Valley rock layer.
Is a fast-grown crystal less “real”? No. Lab-grown quartz is chemically and structurally quartz; only the origin is different. See Synthetic vs natural.
Related pieces in the shop
- Bismuth Crystal Chunk, 1 kilo (fast growth)
- Large Double-Terminated Herkimer Diamond, Fort Plain NY (slow growth)
- Milky Phantom Quartz Cluster, New Hampshire (growth pauses frozen inside)
Sources: Van Driessche, García-Ruiz, Tsukamoto, Patiño López & Satoh, “Ultraslow growth rates of giant gypsum crystals,” PNAS (2011), via phys.org, “Slowest crystal growth”; Wikipedia, Cave of the Crystals.
