Garnets

Garnets are type of gems, which former purpose was commanding the fleets and colonies. They didn't appear in the show, but Hessonite was illustrated by Nephrite in "Monster Reunion", also she was  mentioned in "Legs from here to Homeworld". Also Demantoids and Pyropes were mentioned by Blue Diamond in Together Alone. Physycaly all three knowable Garnets had physical appearance in "Light Trilogy".