Unknown Gems

Unknown Gems are Gems who have been visually shown through holograms, drawings, named, or other methods. They, or their gemstones, have not been officially identified.

"Historical Friction"
There is an unknown Gem seen in the play Steven and Jamie put on in "Historical Friction". She does not appear to resemble any other fusions. It is implied that she is a fusion of some or all of the Crystal Gems. There is also a monster; it is most likely a Gem monster.

"The Answer"
There are many unknown silhouette Gems in The Answer in Garnet's flashback.

"Same Old World"
There are a few unknown Gems featured in Lapis's flashback.

"Monster Reunion"
There are a few unknown Gems featured in Centipeetle's flashback.

"Bismuth"
These are the "other Crystal Gems" who were mentioned by Bismuth, except for Nephrite, which is most likely a Homeworld Gem. They appear to be her close friends. Their statuses are unknown.
 * "Crazy Lace" (Crystal Gem, mentioned by Bismuth)
 * "Biggs" (Crystal Gem, mentioned by Bismuth)
 * "Snowflake" (Crystal Gem, mentioned by Bismuth)
 * Nephrite (Homeworld ship pilot, mentioned by Bismuth to Pearl)

"Beta"
At the Beta Kindergarten, Peridot mentions that a certain "Carnelian" came out of her hole sideways.

Attack the Light
There is an unknown Gem from Steven Universe: Attack the Light.

Steven Universe Comic
There are some unknown Gems from the Steven Universe comics.

Trivia

 * The unnamed Gem warrior from "Sworn to the Sword" is voiced by Michaela Dietz. This may imply she is an Amethyst or some type of Quartz.