Kromikerroksia

Kromikerroksia is a term used in geological literature to describe a class of laminated, chromium-rich rocks characterized by alternating layers of chromium-bearing laminae and silicate-rich laminae. The layering is typically fine-scale, ranging from a few millimeters up to several centimeters, and can extend over substantial outcrop sections. The darker laminae commonly contain chromium-bearing minerals such as chromite, while lighter laminae are dominated by silicate minerals such as feldspars, micas, or amphiboles, within a matrix of olivine and pyroxene in ultramafic to mafic rocks.

Formation and interpretation: Kromikerroksia is interpreted as a product of metasomatic alteration and magmatic differentiation in crustal rocks, where chromium-rich fluids or melts crystallize in alternating episodes, creating the layered texture. Conditions favoring such layering include episodic changes in temperature, pressure, and chemical milieu during intrusion or regional metamorphism.

Distribution and occurrence: Documented occurrences are reported in select ultramafic intrusions and layered complexes, with several examples described in temperate or polar regions. Outcrops show visible lamination in hand specimens and via thin section. The term is not universally adopted in international mineral nomenclature, and some geologists regard Kromikerroksia as a textural variety within established rock types rather than a separate lithology.

Name and status: The name derives from Finnish kromi (chrome) and kerroksia (layers). Since its introduction in the early 21st century, it has remained a topic of discussion and clarification in relation to classification schemes for chromium-rich rocks.

Related concepts include chromite, layered silicate systems, lamination in rocks, and metasomatic processes.