The outer stone casing might also just be the rock farmer equivalent of a fruit rind with all the flash bits insdie, like the big rock Rarity found when she discovered her cutie mark. That said, there is a fair bit more call for farm-scale production in more conventional stone, I expect, and "A bumper crop of rocks!" makes for a better joke anyway as anyone with so much as a little ornamental flower garden will understand.
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‎noli esse culus
‎noli esse culus