How to obtain an Earth Crystal in Stardew Valley

I've been playing Stardew Valley on my Xbox One for about a week or so, and I can't seem to get earth crystals. I see them commonly in the mines, but I have no clue as to how to actually get them as an item. I cant seem to use any of my tools on them (the same goes for quartz). I don't desperately need them, but it'd be nice to know how to get them, and if anyone knows how to please let me know.