Bone is intended for the Necromancer class. Although the number of mods on this item is sparse, they all have the right idea: +skills, a huge mana bonus, and decent resistances. Note that the chance to cast Bone Armor will override existing Bone Armor. Some players may consider the pair of Um runes to be a little pricey, but it is still quite easy to construct, and the overall bonuses can be quite viable for any character.
15% Chance To Cast level 10 Bone Armor When Struck
15% Chance To Cast level 10 Bone Spear On Striking
+2 To Necromancer Skill Levels
+100-150 To Mana (varies)
All Resistances +30
Damage Reduced By 7