Aplite is an intrusive rock containing the quartz and feldspar mineral; aplite rocks have a grey, whitish, or pinkish color, and they are excellent (Welch, 2011). Additionally, aplite crystals are quite defective and solidify almost immediately, but they fit closely similar to the mosaic grains; however, the grains for aplite crystals are very small and can only be visible using a magnifying lens (Welch, 2011).
While coal rocks are sedimentary rocks formed through biochemical reactions and are mostly related to shale, sandstone, and limestone (Welch, 2011), they differ from aplite in color since they are black, dark brown, or gray and also have a glassy texture that is unique (Welch, 2011). Commonly the coal rocks contain various minerals such as graphite, pyrite, and mineraloid. They have diverse uses since they act as sources of energy, source of carbon, and even act as lubricants (Welch, 2011).
On the other hand, quartz and feldspar are both minerals on earth surfaces but differ in various ways; quartz, for instance, is mostly found in sedimentary and metamorphic rocks while feldspar is found in granite bodies; the Quartz minerals are said to be much harder than feldspar (Mosquera, 2008).
Reference
Mosquera, D (2008). A simple method to separate quartz and feldspar. Web.