Kivilajina

Kivilajina is a term used in geology, particularly in Finnish-language sources, to describe a conceptual category of rock defined by its mineralogical composition rather than solely by its lithological appearance. The word combines kivi (rock) with lajina (type or kind) and is used to discuss classification schemes that prioritize mineral assemblages over traditional rock names. In this sense, a kivilajina is not a single rock specimen but a defined composition range that could occur in different tectonic settings.

Definition and characteristics: A kivilajina is characterized by a dominant set of minerals—typically silicates such as feldspar and quartz, with a defined suite of accessory minerals—and by a texture consistent with rapid crystallization or metamorphic re-equilibration. The precise thresholds are defined in educational or research contexts and may vary between formulations. The concept aims to unify rocks that share mineralogical signatures across igneous and metamorphic domains.

Formation and occurrence: The term arises in discussions of classification and is not tied to a single formation process. In some Finnish texts it is presented as a way to discuss rocks that arise through mixed or transitional histories, such as regions experiencing both igneous differentiation and metamorphism. There are no widely cited, globally standardized localities for kivilajina; used mainly in theoretical or classroom contexts.

Significance: Kivilajina underscores a trend toward composition-based rock classification and away from purely textural categories. It remains a niche concept with limited international adoption and is primarily of pedagogical value in Finnish geology education.