Source: Keys from the Golden Vault

Wondrous Item, Legendary (Requires Attunement)

This gemstone contains an unstable extradimensional rift. Its facets are ribboned with iridescent veins that seem to move of their own accord. Five types of shard solitaire are known to exist, each one a different type of gemstone, as shown in the Shard Solitaire Types table.

Rift Step. As a bonus action, while wearing or holding the shard solitaire, you can teleport yourself, along with anything you're wearing or carrying, to an unoccupied space you can see within 30 feet of yourself.

When you use this property, you can tap into the unstable power of the stone's extradimensional rift to increase the teleport distance by up to 30 feet, but if you teleport more than 30 feet using Rift Step, you must succeed on a DC 16 Constitution saving throw or take 3d10 force damage immediately after you teleport.

Spellcasting. The stone has 6 charges and regains 1d6 expended charges daily at dawn. The Shard Solitaire Types table lists the spells common to all shard solitaires, as well as the spells specific to each kind of stone. As an action, you can cast one of the stone's spells by expending the requisite number of charges, requiring no material components (save DC 16).

Shard Solitaire Types
Shard Solitaire Spells
All Banishment (3 charges; the target is banished to the stone's extradimensional space for the spell's duration), Mirror Image (1 charge)
Black Sapphire Blight (3 charges), Finger of Death (6 charges)
Diamond Ice Storm (3 charges), Simulacrum (6 charges; the duplicate created by the spell has the same number of hit points as the creature it imitates)
Jacinth Fireball (2 charges), Fire Storm (6 charges)
Rainbow Pearl Prismatic Spray (6 charges), Water Breathing (2 charges)
Ruby Fly (2 charges), Teleport (6 charges)