Aplite

Aplite is a fine to very fine-grained sugary-textured rock of granite composition. It is composed of feldspar, mica and quartz with minor amounts of garnet and tourmaline. Aplite is believed to form via rapid crystallisation from decompressing superheated water vapour, saturated with dissolved granite, deep underground. Most aplite bodies form veins called dikes a few centimetres to meters in thickness. Some aplite occurrences are associated with economic ores of tin and tungsten.