Apr 23 2014
Lamprophyre is a group of ultrapotassic, igneous rocks that consist of phenocrysts of mica - particularly biotite or phlogopite - and amphibole, such as pargasite or hornblende. It also includes smaller quantities of melilite and clinopyroxene. It is an alkaline silica-under-saturated mafic, or ultramfic, rock with high percentages of nickel, chromium, sodium oxide, potassium oxide, and magnesium oxide.
Lamprophyre is characterized by a porphyritic texture, in which phenocrysts are enclosed in a fine- grained to dense groundmass. The groundmass consists of perovskite, Fe-Ti oxides, glass, pyroxene, amphibole, mica, melilite, monticellite, carbonate, feldspathoids, alkali feldspar, and plagioclase. Chemically lamprophyre is distinct, due to its low silica content and high iron, alkali, and magnesium content. The most common lamprophyres of large masses include diorite and granite.
There are different types of lamprophyres based on their mineralogy, which include spessartite, vogesite, fourchite, monchiquite, camptonite, alnoite, and minette. Lamprophyres have a greater affinity towards lamproites and kimberlites. These igneous rocks are usually present as hypabyssal intrusions, such as sills and dykes, and are associated with granitic intrusions.