alkalireaktiv

Alkalireaktiv is a term used in petrology to describe certain igneous rocks that contain a higher proportion of alkali feldspar relative to plagioclase feldspar. This classification is part of a broader system for naming and categorizing rocks based on their mineral content, particularly their feldspar composition. In essence, alkalireaktiv rocks are richer in sodium and potassium-bearing feldspars than rocks that fall into other categories.

The designation of a rock as alkalireaktiv is often determined through modal analysis, where the proportions of different minerals are counted. Rocks classified as alkalireaktiv typically fall within specific fields on petrochemical diagrams, such as the QAPF diagram, which plots the relative amounts of quartz, alkali feldspar, plagioclase feldspar, and feldspathoids. The term implies a certain geochemical signature, indicating that the magma from which the rock crystallized was relatively enriched in alkalis, particularly sodium and potassium.

Examples of alkalireaktiv rocks include certain types of granite, syenite, and their volcanic equivalents. The specific mineral assemblage and overall texture will further define the rock's precise name within the alkalireaktiv group. Understanding the alkalireaktiv nature of a rock can provide insights into the geological processes, such as magma source and differentiation, that led to its formation.