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How do crystals grow?

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Quick answer

Crystals grow when a substance's atoms or molecules deposit onto a tiny seed in an ordered, repeating pattern. This requires a supersaturated solution, a supercooled melt, or a supersaturated vapor. Particles attach at specific lattice sites, building flat faces. The final shape reflects the substance's internal symmetry and the conditions during growth.

Crystals grow when atoms or molecules in a liquid or gas arrange themselves into an ordered, repeating pattern called a crystal lattice. This happens when the solution becomes supersaturated or the melt cools below its freezing point, forcing particles to deposit onto a tiny seed crystal.

Step by step

  1. A small cluster of atoms or a foreign particle acts as a seed crystal.
  2. The surrounding fluid becomes supersaturated or supercooled, so it contains more dissolved material than it can normally hold.
  3. Atoms or molecules from the fluid attach to the seed's surface, aligning with the crystal lattice.
  4. The crystal grows outward layer by layer, with faster-growing faces eventually disappearing.
  5. The final crystal shape is determined by the lattice geometry and the growth conditions.

Key things to understand

  1. A crystal starts as a tiny seed, either a foreign particle or a small cluster of the same substance.
  2. For growth to occur, the surrounding fluid must be supersaturated or supercooled, meaning it holds more dissolved material than it normally can at that temperature.
  3. Atoms or molecules attach to the seed's surface, preferring positions that match the crystal's internal lattice structure.
  4. As more particles join, the crystal grows layer by layer, often forming flat faces that reflect its internal symmetry.
  5. The final shape depends on the substance's lattice geometry and the growth conditions, such as temperature, pressure, and impurity levels.

Labelled diagram

  1. Seed

    A tiny particle or cluster provides a surface for growth.

  2. Supersaturated solution

    The liquid contains more dissolved material than it can normally hold.

  3. Attachment

    Atoms or molecules deposit onto the seed, aligning with the lattice.

  4. Layer growth

    New layers form, and flat faces develop as the crystal expands.

  5. Final crystal

    The shape reflects the internal lattice and growth conditions.

How a crystal grows from a solution

Real-world examples

  • Rock candy forms when a string is dipped into a supersaturated sugar solution and sugar crystals grow on it over days.
  • Snowflakes are ice crystals that grow from water vapor in cold clouds, developing six-fold symmetry.
  • Quartz crystals in geodes grow over thousands of years from silica-rich water inside rock cavities.
  • Table salt crystals form when seawater evaporates in salt pans, leaving behind cubic sodium chloride crystals.

Common mistake

✗ Myth: Crystals grow only from cooling melts, like water freezing into ice.

✓ Fact: Crystals can also grow from solutions, vapors, and even solid-state reactions. For example, snowflakes grow directly from water vapor, and many minerals crystallize from hot, mineral-rich water.

People also ask

What causes crystals to form?
Crystals form when a substance's particles arrange into an ordered lattice. This happens when the substance changes state, such as cooling from a liquid or becoming supersaturated in a solution. The particles lose mobility and lock into positions that minimize energy, creating a repeating pattern.
How do crystals grow in a solution?
In a solution, crystals grow when the solvent evaporates or cools, making the solution supersaturated. Dissolved particles then deposit onto a seed crystal, attaching at lattice sites. The crystal grows layer by layer, often forming flat faces. Stirring or impurities can affect the growth rate and final shape.
Why do crystals have different shapes?
Different substances have different lattice structures, which determine the basic crystal shape. For example, salt forms cubes, while quartz forms hexagonal prisms. Growth conditions like temperature, pressure, and impurities can also modify the shape by favoring growth in certain directions.
What is a seed crystal?
A seed crystal is a small particle or cluster that provides a surface for new atoms or molecules to attach. It can be a speck of dust, a tiny fragment of the same substance, or even a scratch on a container wall. Without a seed, crystal formation may be slow or not happen at all.
Why do crystals have flat faces?
Flat faces appear because atoms pack most efficiently in certain planes of the lattice. These planes grow outward faster than others, eventually dominating the crystal's surface. The angles between faces are constant for a given substance, a fact known as the law of constancy of interfacial angles.
Can crystals grow from a gas?
Yes. When a gas cools or becomes supersaturated with vapor, molecules can deposit directly onto a solid surface, forming crystals. Snowflakes and frost are common examples: water vapor in air crystallizes into ice without passing through a liquid stage.
How long does it take for a crystal to grow?
Growth time varies enormously. Some crystals, like those in instant ice packs, form in seconds; others, like quartz in geodes, take thousands of years. The rate depends on temperature, concentration, and how quickly particles can reach the growing surface.

Part of the guide: Nature & Earth: Living Things and Rocks →