On average the stone will drop:
an argil oppressor 37%
a cleaned brimstone aberrant 33.33%
a brimstone aberrant 26.32%
a whirling sootshadow 25.23%
a galvanized guardian 25%
an arbiter of ash 20%
a brimstone juggernaut 20.00%
a chaotic clay guardian 19.46%
a darkshard guardian 11.11%
an ashen dervish 10%