Basalt

Basalt is one of the strongest blocks in the game and can be found in the ancient resevoirs and in the basaltic crevice you can make make basalt slabs, basalt stairs basalt bricks and basalt pillars with it

Other things you can make with it are:

-Crystal Forge (50 Basalt and 50 Iron Ingot)

-Crystal Mold (50 Basalt and 20 Platinum)

-Hook Shot (10 Basalt, 7 Iron Ingot, 10 String and 2 Sticks)