Slate provides very high mining experience, especcialy pre-20. This means easily getting miner level just with slate. Slate can be mined with a copper pick or better, and is thus accessible all game.
Slate BricksEditSlate bricks have a higher explosion resistance than simple stone, making them a very effective building material. They are crafted by putting 4 slate into a block pattern.
According to the spirit guide "Step stones can be placed on hard stone pillars". This hard stone is slate. a step stone must be placed on a block of slate, and at the same time, slate is used to craft Near Step-Stones, so you will already have some.