Stand next to the ore and hold your interact key to charge up the Everlight. Be careful not to hold it too long, or it will fall behind Stella and you will have to wait for her to pick it back up. It is ideal to release the pickaxe just before it overcharges, or just after it begins to flash.
Some nodes take multiple strikes to break.
In several of the mines, there are treasure chests that can only be accessed by walking into walls. Most of these hidden passages are marked by the lights in the mines.