- Black onyx
- Tiger eye
In variants with an object materials system, many more objects including weapons and armor can be made of gemstone - sometimes referred to as crystal by the game. It is generally a high-quality material for weapons and armor, but such items also very expensive and often hard to come by.
SLASH'EM introduces new types of golem that are made of gemstone - the ruby, sapphire, diamond, and crystal golems. All gemstone golems have a powerful physical attack and a breath weapon; the diamond golem can used a random breath attack, similar to the Chromatic Dragon. All four varieties of golem drop gems of their respective material upon death, with the crystal golem leaving behind a pile of random valuable gems.
In GruntHack, gemstone is the heaviest and most expensive among object materials, but provides a +2 bonus to AC relative to iron armor.
In EvilHack, gemstone functions as it does in GruntHack, but is more light than most metals (save for mithril) and immune to erosion. Gemstone weapons gain a +3 damage bonus if they deal slashing or piercing damage; dwarven-made weapons have a 5% chance of generating as made of gemstone.
The following items have a base material of gemstone:
In xNetHack, gemstone functions similarly to how it does in EvilHack, though no objects have their base material changed to gemstone.
In dNetHack, new gemstone objects like the fossil dark and magicite are introduced. Valuable gems can also be used as focusing crystals for lightsabers to produce different-colored 'blades'; worthless pieces of glass will always result in a red lightsaber.