What is a columnar basalt?

Columnar basalt exhibits massive, vertically standing columns. Although usually hexagonal (six-sided), such columns are polygonal (multi-sided) and may have anywhere from three to 12 sides. They are often so uniform in size and shape that they seem to have been artificially constructed, like giant columns of poured concrete.

Are rock columns made of basalt?

And though these columns are usually made of basalt, that isn’t always the case. Devil’s Tower, in Wyoming (USA), is a good example. It is a huge structure of columns formed in a less common type of rock called phonolite. And rock columns also aren't limited to Earth... rock columns have even been found on Mars.

What are the best basalt flows for column formation?

Columns are well-developed in some of the flows and non-existant in many others. The Roza Flow is the most famous Columbia River Basalt flow for column formation. Notable columns around the world include Devil's Tower in Wyoming and Giant's Causeway in Ireland.

What is columnar jointing of volcanic rocks?

Columnar jointing of volcanic rocks exists in many places on Earth. Perhaps the most famous basalt lava flow in the world is the Giant's Causeway in Northern Ireland, in which the vertical joints form polygonal columns and give the impression of having been artificially constructed.