andesiitides

Andesiitides is a term used in mineralogy and petrology to describe rocks that are primarily composed of andesine, a plagioclase feldspar. Andesine itself is an intermediate member of the plagioclase solid solution series, falling between albite (NaAlSi3O8) and anorthite (CaAl2Si2O8). Rocks classified as andesiitides would therefore have a significant proportion of andesine within their mineral assemblage, often alongside other common volcanic or plutonic minerals depending on the specific rock type.

The term andesiitides is not as commonly encountered as more general rock classifications like andesite or diorite. Andesite is a volcanic rock, typically extrusive, characterized by its intermediate silica content and a mineralogy that often includes plagioclase feldspar (frequently andesine), amphibole, and pyroxene. Diorite, on the other hand, is a coarse-grained intrusive igneous rock with a similar mineral composition to andesite, but it solidifies slowly underground. While andesine is a key mineral in these rocks, the term andesiitides specifically emphasizes the dominance of this feldspar.

The presence and abundance of andesine in a rock can provide clues about its origin and the conditions under which it formed. For instance, plagioclase feldspars crystallize over a range of temperatures and pressures, and the specific composition of andesine can reflect the magma chemistry and cooling history. Therefore, while andesiitides might be a less frequently used term, understanding the role of andesine is fundamental to classifying and interpreting many igneous rocks.