Chests can be bought with in-game currency (picks or runic). There are 2 types of chests: Small chests and Large chests.
Small Chests Edit
Small chests are bought with picks, and yield 5 different variants of blocks (each different variant has 9-11 for rare blocks and 11-24 common blocks yielded), a small chance of a pickaxe, companion, and a chest treasure. The cost of a small chest is about 18,000 times your pps.
Large Chests Edit
Large chests cost 100 runic, and yield significantly more blocks. It yields 5 different variants of blocks(each different variant has 21-71 for rare blocks and 74-282 common blocks), increased chance for a pickaxe, companion, and chest treasure.