|Maybe not quite this heavy|
When used against creatures from the material planes, the slowness of the weapon's "blade" is such that the damage done is only 25% real, and 75% temporary (recovering at the rate of 1hp per turn). However, if the target is reduced to 0 or less hit points in this manner, regardless of retaining "real" hit points, then it is turned to stone with no saving throw. Magic resistance might save the victim, rolled "as is" on each applicable strike.
When used against creatures native to the elemental plane of earth, the sword is simply treated as a +3 weapon with no special abilities.
Against creatures from any other plane, the weapon is treated as a club for weapon Vs armour and does 1d6 of normal damage with no petrification.
General properties are as follows:
Form: broadsword made of stone
Weapon Vs Armour: as footman's mace against material beings; as broadsword against elemental Earth beings; as club against all others
Space required: 4'
Speed factor: 12
If you don't use speed factors, limit use to STR 12 and above and bear in mind that characters under 100lbs weight can not use weapons with encumbrance of 200 or more.
Gp value: 8000
Xp value: 1200