Harvestable Crystals. Maybe a random probability of different types of crystal that you can obtain from breaking open a rock. Crystals could have different uses, properties - like a mild healing / mood boost, etc. Maybe a property similar to compost (but less potent) . Crystals could be recharged in the sun (menu option with a significant time wait (thinking 1-3 days) or have a set number of uses, after which they become inert (just use for decor, or recycle? compost?) . Maybe different levels of 'power' and common/unusual/rare / super rare levels or something. Not sure how you come about the rocks - maybe purchase and/or hunts/events? Almost maybe like gacha -- where you don't know what you'll get - it's a random chance to get one of a set # of crystals with different properties. If they're re-chargable, they could be traded.