Chip of Creation
Wondrous Item, artifact (requires attunement)
This solid, hand-sized flake of rock is a minor piece of the Stone of Creation and contains a portion of its power.
Linked Room
Each chip of creation is inextricably linked to its own demiplanar room, as per the demiplane spell. This room exists as long as both this chip and the Stone of Creation do. A door to the room only exists when created using a demiplane spell, whether a chip of creation is used in the casting or not.
Demiplane
While attuned to a chip of creation, you can cast demiplane at will but only to reach the demiplanar room associated with that chip of creation or another demiplane that you know the nature and contents of, and only if the target demiplane was created by another piece of the Stone of Creation.
Destroying a Chip
A chip of creation is an artifact in its own right and impervious to most damage, but a disintegrate spell is sufficient to destroy it. After it has been attuned once, a chip that has gone 1d4 + 1 days unattuned becomes an inert, powerless bit of rock.
If the Stone of Creation is destroyed, all its chips break attunement, lose all magical properties, and linked demiplanar rooms cease to exist at once. Creatures or objects within the room are instantly expelled into the immediate vicinity of the destroyed chip.
If it reaches the Elemental Chaos or is struck by a forked, metal rod attuned to the Elemental Chaos (as per the plane shift spell), a chip is destroyed.
Source: Adventures in the Forgotten Realms: A Verdant Tomb p. 11, Adventures in the Forgotten Realms: From Cyan Depths p. 13