These single-pronged blue crystals look very much like large blue crystals, except for being medium-sized. They are created at the time of a world's generation and are found underground in small caves. They often appear near another blue crystal, and are somewhat rarer than their small-sized cousins. Like other blue crystals, they give off a blue glow.
Despite their beauty, these crystals deal the same damage as small crystals and other dangers like stalagmites and stalactites.
How to Obtain
All crystals can be mined with any pickaxe.
As of November 2013, these crystals are decorative only. They're also used in trading. Since they're light-emitting, they can also be used as a dramatic alternative to traditional fixtures to illuminate an area.
Medium and large blue crystals have been in the game since crystals were first implemented, but have only been collectible into inventory by players since October 2013. Before that, mining a medium or large blue crystal would drop only one small blue crystal into inventory.
As of November 2013, medium and large blue crystals are the only crystals other than small reds and purples that are solid (i.e., have collision).