noun-modifying (irregular)
polycrystalline
Technical term used in materials science and crystallography to describe a solid composed of many small crystals or grains. Often used attributively (prenominally) as in 多結晶性シリコン (polycrystalline silicon).
See also: 非結晶性
Polycrystalline silicon is widely used in solar cells.
This material has a polycrystalline structure.
非結晶性 (amorphous/non-crystalline) is the opposite, describing solids without long-range crystal order. 多結晶性 refers to many small crystals, while 非結晶性 refers to no crystals.
単結晶 (single crystal) is a solid with a continuous crystal lattice, as opposed to 多結晶性 which consists of many small crystals.
Compound of 多 (many), 結晶 (crystal), and 性 (property/nature). A straightforward technical coinage.