How crystals grow from a solution
Crystals can grow when a solution contains more dissolved material than can remain dissolved under its current conditions. Particles join an ordered structure, often beginning at a tiny nucleus or existing crystal. Evaporation or cooling can create these conditions, depending on the substance.
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Particles joining an ordered pattern
A crystal has a repeating internal arrangement of atoms, ions or molecules. Growth occurs when particles from the surroundings attach in positions consistent with that structure.
In a solution, crystallisation becomes possible when conditions favour the solid forming. Evaporating solvent increases concentration, while cooling reduces the solubility of many, though not all, substances.
Nucleation is the initial formation of a small stable crystal region. Once a suitable crystal surface exists, additional particles can attach and extend it.
- Evaporation can bring a solution towards saturation.
- Further change can favour crystal growth.
- Existing crystals provide surfaces for attachment.
Growth conditions influence size and appearance. Many nuclei can divide the available material among numerous small crystals, while fewer growing sites may allow larger ones to develop.