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.
Aplites are usually very fine-grained, white, grey or flesh-coloured, and their constituents are visible only with the help of a magnifying lens.
The aplites of granite areas, for example, are the last part of the magma to crystallize, and correspond in composition to the quartzo-felspathic aggregates which fill up the interspaces between the early minerals in the main body of the rock.
The essential components of the aplites are quartz and alkali felspar (the latter usually orthoclase or microperthite).
Aplite in petrology, the name given to intrusive rock in which quartz and felspar are the dominant minerals.
Dykes and threads of aplite are very frequently to be observed traversing granitic bosses; they occur also, though in less numbers, in syenites, diorites, quartz-diabases and gabbros.
Riebeckite-granites (paisanites) have close affinities to aplites, shown especially in the prevalence of alkali felspars.
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