APLITE
Aplite
Aplite in petrology, the name given to intrusive rock in which quartz and feldspar are the dominant minerals. Aplites are usually very fine-grained, white, grey or pinkish, and their constituents are visible only with the help of a magnifying lens. Dykes and threads of aplite are commonly observed traversing granitic bodies; they occur also, though less frequently, in syenites, diorites, quartz-diabases and gabbros.The above text is a snippet from Wikipedia: Aplite
and as such is available under the Creative Commons Attribution/Share-Alike License.