Stone on healing ears is a no
As another porous material stone easily traps bacteria on the surface which for fresh piercings is the quickest way to an infection. You should also avoid stone piercings if your healed ears have become irritated or you have overly sensitive skin as it could cause an irritation.
Regarding this, what are the gauge sizes for ears?
Standard ear piercings are usually pierced at 20g or 18g. Gauge sizes go up (or down, depending on how you look at it) in even numbers from there, so the next largest size from an 18g is 16g, then 14g, then 12g, and so on. When you get to 0g, the next size is 00g (pronounced “double zero gauge”).