Moon Weed is a very common block found only in The Moongardens. It
Moon weed block

A Moon Weed Block.

is the equilivant of Dirt in the Overworld. It is as easy as mining Netherack with a stone pickaxe. It has low resistance, and is not suggested to build houses out of. If you place Moon Weed in The Nether, it will immediatly catch fire, explode and disappear like beds when you try to sleep on them.