Shell issues

[robandcath]

Recently a friend had a snail (achatina reticulata) that died, it's never had good growth despite her other snails growing well. Upon looking inside the snails shell she noticed that the snail had what looked like hard rough deposits inside the shell where the mantle should be.
Was wondering if anyone had any information as to what this could be and possible causes.

[etana]

If all the other snails grew normal shells, it sounds to me like an issue/illness the one snail may have had since birth. If there were more ill snails I'd check if there possibly was too much calcium in the tank (mixed in with food instead of a separate source) but this doesn't sound like that really.