Minette thin section photomicrograph, cross polarized lighting. Sedbergh, Yorkshire, UK

Minette is a type of mineral deposit, consisting of iron ore of sedimentary origin. Minette contains biotite and orthoclase. Lamprophyres are a group of rocks containing phenocrysts, usually of biotite and amphibole (with bright cleavage surfaces), and pyroxene, but not of feldspar. They are thus distinguished from the porphyries and porphyrites in which the feldspar has crystallized in two generations. They are essentially dike rocks, occurring as dikes and thin sills, and are also found as marginal facies of plutonic intrusions. They are usually dark in color, owing to the abundance of ferro-magnesian silicates, of high specific gravity and liable to decomposition. For these reasons they have been defined as a melanocrate series (rich in the dark minerals); and they are often accompanied by a complementary leucocrate series (rich in the white minerals feldspar and quartz) such as aplites, porphyries and felsites.