Aplite dike


This is a piece of an aplite dike cutting through granite host rock. Aplite is an intrusive igneous rock in which the mineral composition is the same as granite, but in which the grains are much finer, under 1 mm across. This sample might also be called alaskite. Alaskite is a a “leucocratic” (meaning light colored) granite of medium or fine grain composed chiefly of quartz and alkali feldspars.
River cobble, San Benito River, Hollister, CA.
https://gotbooks.miracosta.edu/rocks/igneous/33.html 2/2/2021