What is cirrocumulus clouds made of?

Like other clouds, cumulonimbus clouds are made of water droplets and ice crystals. They're often associated with severe weather such as thunderstorms.
Mostly a lot of condensed water droplets.
Cumulonimbus clouds are made of water droplets in their lower portions and ice crystals in their upper portions.
Pretty much all clouds are made of water vapor (steam) that evaporates from lakes or rivers.