Diamond Communicator

The "Diamond Communicator" is a octahedral gem-like object first seen in episode "It Could've Been Great". It stood on the chair on the top floor of the Moon Base. Peridot secretly took it with her as the Gems were leaving the base.

Its facets appear to be colored white, yellow, blue and pink, signifying the Great Diamond Authority.

It was later revealed in "Message Received" to be a communicator, offering a direct line to any member of the Great Diamond Authority. Peridot made contact with Yellow Diamond through the device and attempted to convince her to spare Earth in favor of more eco-friendly uses of its resources. When Yellow Diamond snubbed Peridot's request, preferring to see Earth destroyed by the Cluster, Peridot terminated her allegiance to her and the communication. Yellow Diamond responded by detonating the communicator remotely, but it was bubbled by Steven and knocked away by Garnet before the explosion could hurt anybody.

Appearence
The communicator appears to be a 3D rhombus shape with the colors of the corresponding diamonds, yellow, blue, white and pink.