Don't Panic Geocast

Forms in fractures of rocks already in place, so it an INTRUSIVE feature Form at right angles to the direction of extension in the area - nature’s frac jobs Can be super thin or super thick, but generally are self-consistent Can have multiple periods of injection or even multiple compositions of injection over time Can get en echelon patterns, rings, and cones (last two common with caldera volcanism) Magmatic are the most well known and form when magma flows into a crack and cools into a sheet. The igneous rock is generally more weathering resistant so we get cool weathering features Can be rhyolitic, but mostly basaltic Rate of cooling determines grainsize (slow = big) and big near the center Can have columnar jointing Big phenocrysts orient with flow direction - cool! AMS studies show this. These are awesome when you get them radially around a volcano! Horizontal dikes are called sills Clastic dikes are formed by sediments episode 177 (https://www.dontpanicgeocast.com/177) Can be formed with fluid pressure