macrocrystal

Macrocrystal is a term used in mineralogy and materials science to describe a crystal that is large enough to be seen with the naked eye. It refers to crystals whose individual lattice is visible as a single, well-formed crystal, as opposed to materials composed of many microscopic crystals (microcrystalline) or cryptocrystalline substances whose grains are too small to resolve even with low-magnification techniques. In practice, macrocrystals are typically those with dimensions of a few millimeters or larger, and many reach centimeters or more in size.

Natural macrocrystals form under conditions that favor uninterrupted crystal growth, such as slow cooling of molten rock in pegmatites, low nucleation density, or open geochemical environments that allow sustained growth. Common examples include quartz crystals, calcite rhombs, gypsum crystals, and various feldspars and micas. Synthetic macrocrystals are produced in laboratories or industrial settings by controlled solution growth, melt growth, or vapor deposition, with attention to purity and temperature gradients to minimize defects.

Macrocrystals are valued for their optical quality and cleavage characteristics; their large size often allows straightforward measurement of properties by X-ray diffraction, polarized light microscopy, and other techniques. However, macrocrystals may exhibit growth zoning, twinning, or internal defects that affect clarity and mechanical strength.

Because the term is size-based rather than mineral-specific, macrocrystal is used across geology, gemology, and materials science to describe crystals that are visible to the naked eye and have a predominantly single-crystal character.