Hienokiteisiä

Hienokiteisiä is a Finnish geological term used to describe rocks that have a fine-grained or microcrystalline texture. The word is formed from hieno (fine) and kide (crystal) with the adjectival suffix -inen, and the plural form hienokiteisiä is used when referring to multiple rocks or rock units.

In practice, hienokiteisiä describes textures in which individual mineral crystals are too small to be resolved with the naked eye. In igneous rocks this corresponds to an aphanitic or microcrystalline groundmass, as seen in many basalts, andesites, rhyolites and other volcanic rocks. In metamorphic rocks, fine-grained textures occur in hornfels, slate, phyllite and related rocks, where crystals are small and evenly distributed.

Typical grain-size ranges are used for characterization: fine-grained textures generally have crystals smaller than about 1 millimeter, while microcrystalline textures may feature crystals in the 0.01–0.1 millimeter range; cryptocrystalline textures are even finer and often require microscopic examination. Determination of the texture commonly relies on optical microscopy or scanning electron microscopy to identify crystal sizes and relationships.

The term is widely used in Finnish-language geology to describe texture without prescribing a strict mineralogical assemblage. It serves as a descriptive qualifier across rock types, helping to distinguish rocks with small, dense crystal networks from coarser varieties like phaneritic rocks.

See also: aphanitic texture, microcrystalline texture, cryptocrystalline, phaneritic.