Diorite

Diorite, a basic crystalline igneous rock, including many of those formerly known as greenstone. It consists of plagioclase felspar, generally white, and hornblende, dark green or black, in varying proportions. There is usually some magnetite and minute needles of apatite present, and some varieties contain quartz or mica. Corsite, otherwise known as napoleonite or orbicular diorite, occurring in Corsica, contains globular aggregations an inch or two across, and is made up of greyish anorthite, blackish hornblende, and some quartz. Kersanton, or mica-diorite, has mica partly replacing its hornblende. Diorites are mostly granitoid in texture, but may be porphyritic. Their average silica percentage is 54 and specific gravity 2-95. They occur in Palaeozoic volcanic necks as eruptive rocks.