Basalt

A volcanic stone most commonly formed from the rapid cooling of lava at Earth’s surface. Basalts can date back billions of years to the time of the formation of the earth itself. A fine-grained, dark grey, hard and dense stone, Basalt underlies more of Earth’s surface than any other rock type and makes up most of the sea floor.
Perfect for exterior use in environments with assaulting freezing and thawing conditions.