Can't seem to figure out what this block is...

[kidkaboozle]

Hello, so I've started playing Terraria recently, and about a week ago I'm just digging around in the underground and I happened upon a crimson and black 2x2 block. I can mess around with its shape using a hammer, but cannot break it with my lead pickaxe. I have been just scouring the web for what on earth this block could be and I cannot seem to find a match, so I figured I'd bring it here to see if ya'll could tell me.

 

[shobiwan77]

...and I happened upon a crimson...

Exactly what you said. This is an ore block that relates to the Crimson biome. It's called crimtane ore, and is a reasonable amount better than gold/platinum ore. You can read more about it here: http://terraria.wiki.gg/Crimtane_Ore

 

[Dylan Donut]

Does anyone know what this is?

 

[Nemo]

Does anyone know what this is?

https://terraria.wiki.gg/War_Table

 

[Mental Mouse]

As noted above, that is Crimtane ore, but you aren't going to break it with lead. Early game, you'll need the Reaver Shark or explosives.

It's pretty scarce in the ground too -- you'll need to beat a few bosses before you have enough to make stuff with, and a lot of the stuff you can use it for will also need Tissue Samples from the Brain of Cthulu.

 

[Drake katchadorian]

Yep