Straight up make a BOULDER. (DIY Realistic Rocks from Concrete)

SHOP LINK: https://shop.crafnation.com/

This is a DIY “boulder”, made using a simple form and concrete, with coloring of your choice.
“‘Boulder’ (noun): a large rock, typically one that has been worn smooth by erosion.”
OXIDE COLOR POWDERS:
http://amzn.to/2viwVXu
http://amzn.to/2vDNGxu