What is "crystallite"

Crystallite \Crys"tal*lite\ (kr?s"tal-l?t), n. [See Crystal.] (Min.) A minute mineral form like those common in glassy volcanic rocks and some slags, not having a definite crystalline outline and not referable to any mineral species, but marking the first step in the crystallization process. According to their form crystallites are called trichites, belonites, globulites, etc.

n. A small region of a solid that consists of a single crystal; a grain

n. any of numerous minute rudimentary crystalline bodies of unknown composition found in glassy igneous rock

Polycrystalline or multicrystalline materials, or polycrystals are solids that are composed of many crystallites of varying size and orientation. Crystallites are also referred to as grains. They are small or even microscopic crystals and form during the cooling of many materials. Their orientation can be random with no preferred direction, called random texture, or directed, possibly due to growth and processing conditions. Fiber texture is an example of the latter. The areas where crystallite grains meet are known as grain boundaries.

Most inorganic solids are polycrystalline, including all common metals, many ceramics, rocks and ice. The extent to which a solid is crystalline ( crystallinity) has important effects on its physical properties. Sulfur, while usually polycrystalline, may also occur in other allotropic forms with completely different properties. Although crystallites are referred to as grains, powder grains are different, as they can be composed of smaller polycrystalline grains themselves.

While the structure of a ( monocrystalline) crystal is highly ordered and its lattice is continuous and unbroken, amorphous materials, such as glass and polymers, are non-crystalline and do not display any structures as their constituents are not arranged in an ordered manner. Polycrystalline structures and paracrystalline phases are in between these two extremes.