Basalt
Basalt is a stone-esque block in the hit indie game Minecraft. It really rocks!
Basalt
This form of basalt is found in the aptly named Basalt Delta biome in the Nether. Interestingly, it can be found as far deep as Y = 0! Provided no Blackstone is in the way, of course. It's blast resistance makes it a very useful block for building in the nether, as all it's forms take Ghast fireballs like no problem. Thanks for being so helpful, Basalt!
Polished Basalt
This form can't be found naturally anywhere, but it can be crafted by putting four Basalt together in a square formation, or by putting one basalt into a Stonecutter. (i think, don't quote me on that) It inherits all of the features Basalt has, including it's directional placement, which is similar to logs and pillars of any kind. As such, it is simply an alternative to standard Basalt. How quaint!
Smooth Basalt
This form can be found naturally surrounding Amethyst Geodes, right before the layer of Calcite. It can also be made by smelting Basalt in a Furnace, similar to Stone and Smooth Stone. Unlike Smooth Stone, however, it cannot be made into anything else, like slabs, similar to the other forms of Basalt. It loses it's directional placement, but still keeps the blast resistance. It's alright.