mafic nepheline orthopyroxene orthoclase enstatite magnetite igneous pyrite silica leucite ultramafic sulfide clays oxides calcite metamorphic serpentinite albite peridotite dolomite feldspars carbonate magnesium minerals gabbro garnet basalts phenocrysts sphalerite scapolite sanidine melilite granites quartz schists schist carbonates goethite manganese