Crying obsidian can be mine by a simple wooden pickaxe

I have found a ruin portal, only one block missing(in the chest I have 2 block of obsidian) but the crying obsidian was on the portal so I have removed it... First I make with hand but noticed it would be more easier with a pickaxe so... I have make a wooden one I started mining and I got the crying obsidian block.... With a wooden pickaxe!!