Yellow Diamond

"Yellow Diamond" is a Gem who was first mentioned in "The Return".

Jasper/Peridot/Lapis Lazuli
Yellow Diamond seems to hold some sort of authority, as Jasper and Peridot needed to report to her. As they seem to obey her, Lapis Lazuli and Peridot feared her name.

Gemology
Gemstone Information
 * Diamonds are the stones of truth and victory.
 * Diamond is the transparent, gemstone-quality crystalline form of carbon and it is indeed the hardest known natural substance on earth.
 * Diamonds are typically known to be colorless or 'white', but the most common colors are yellow and brown.
 * Diamond is the official modern birthstone for April, and it is also used as an official sixty year anniversary gemstone.