Stoneskin spell description says it's Abjuration. Scribing station asks for Abjuration ink.
Greater Stoneskin description says it's Transmutation. Scribing station asks for Transmutaion ink.
However, the Greater version of a spell should be the same as the normal one, as it's basically a stronger version.
Weird thing is, that the original NWN description also has this discrepancy. Regular stoneskin being abjuration, greater being transmutation.
Both should be Transmutation I think (barkskin is also Transmutation) as your skin gets transformed.