Karkeakiteisiä

Karkeakiteisiä is a term used in Finnish geology to describe rocks or mineral aggregates that display a coarse-grained crystalline texture in which individual crystals are readily visible to the unaided eye. The word combines karkea "coarse" and kide "crystal," with the adjectival suffix -inen and the plural suffix -isiä, and it is primarily used to characterize the texture of igneous and metamorphic rocks in field and lab notes.

Definition: A karkeakiteinen texture typically refers to grains larger than about 0.5 millimeters, commonly ranging from millimeters to several centimeters, arranged in an interlocking mosaic. The principal minerals are often feldspar and quartz, with mica or amphibole inclusions in some varieties.

Formation and occurrence: The texture results from slow cooling of silica-rich magmas in plutonic settings (granitoids, pegmatites) and from metamorphic recrystallization under high-grade conditions. Karkeakiteisiä textures are especially common in coarse-grained granitoids and pegmatites and may preserve evidence of the original magma or metamorphic conditions.

Physical properties: Rocks with this texture typically show well-formed crystals, a low to moderate porosity, and a color range from light to dark, depending on mineralogy. Hardness is commonly in the range associated with quartz and feldspar, with occasional mica-rich interlayers that influence cleavage.

Significance: The presence of a karkeakiteisiä texture helps geologists distinguish between slow-cooling plutonic assemblages and other textured rocks. It informs interpretations of cooling history, tectonic setting, and crustal evolution, and it aids in correlating rock units across geologic maps.

See also: coarse-grained texture, pegmatite, granitoid, granulite.