You see small rounded grains of quartz and feldspar about the size of a pinhead. The grains are not interlocking. Columnar joints are vertical cracks that can form in volcanic rocks to produce columns. Spheroidal weathering of plutonic rocks results from rounding of corners and edges of exposed rock by weathering processes. Minerals crystallizing from a cooling silicate magma will tend to be less and less polymerized through time.
Pegmatite is a very coarse-grained igneous rock made up mostly of feldspar and quartz.
Volcanoes that erupt rhyolites are generally more explosive than volcanoes that erupt basalt. Volcanoes associated with subduction zones, such as the Cascade Volcanoes in the Pacific Northwest, mostly erupt liquid lava. Convection of the mantle is one mechanism scientists have proposed as being the cause of plate tectonics. Cations are positively charged, whereas anions are negatively charged. Hydrolysis, oxidation, and dissolution are all examples of mechanical weathering.