Rocks seem to be an oft-requested topic for my demonstrations.  Today, I took the workshop out to the Head Harbour Lightstation.  Although most people go there for the lighthouse, I go there for the rocks.  At late morning, the rocks sport deep shadows - perfect for a rock demo!
I chose to zoom in to capture a rocky outcrop with some interesting color.  Orange lichen dappled the tops, and the shadowed sides of the rocks were full of color.
"Warning - Strong Current"5x7, oil, en plein air
Here are the steps I take with rocks:
- Outline the basic shapes
 - Draw in the major dark accents (typically, cracks)
 - Block in the shadowed parts
 - Block in the mid-values
 - Block in the lights
 - Restate the major dark accents
 - Add light highlights
 
By the way, this one is called "Warning - Strong Currents" because that's what the sign says on the left.  The painting is of the middle island that one would cross on a hike out to the lighthouse.  This hike is possible only at low tide.  At any other time, a strong - and very cold - current races through the gap.