The geology of the north shore of Lake Superior has a variety of rock formations. As my wide-eyed four-year-old grandson said, "These rocks on our beach were once red hot lava!"
I always thought it was more fun to draw the rocks were the lava had cooled more slowly into "squarish" shapes. My sketchbooks are full of these more linear formations. If you are just starting to draw rocks, these simple shapes are the ones to start on. Our beach cooled more quickly so the basalt did not have the time to form into large crystal shapes. Instead it is lumpy and irregular and full of holes and cracks. Not as graphic looking but very interesting. the trick is to simplify.
Here are a few pen and ink drawings of our lumpy beach. The lake is indicated by watercolor washes in a variety of blues.