Several years ago a client asked me to build them a “Columnar Basalt” water feature out of artificial rock. At the time, I had never seen or even heard of columnar basalt before. He gave me a few pictures and a bit of a description:

They are a naturally occurring stone column. Mostly octagonal or six sided. They are usually in a cliff structure that sometimes shows severe erosion angling or sloping on their tops. Although sometimes they are in perfect condition, leaving them symmetrical with clean lines. They look just like they were somehow man made. Sometimes they break free from their cliff and fall off in single columns or chunks of several columns still stuck to one another. Often when they break they create a concave top like a bowl.

So I took his information and built this artificial columnar basalt water feature: