Cluster Gems

"Cluster Gems" are forced fusions of former Crystal Gems. They were supervised by Peridot, and created through unknown means.

Appearance
The Clusters take the form of limbs joined together to other appendages. The limbs are of mismatched colors, such as dark and light blue, rust, violet, olive green, mint, and dull yellow, indicating that they originally belonged to different gems. The other end has four feet which are connected by color to the 'fingers' but not the 'thumb'.

A giant variant of a Cluster appears to be comprised entirely of limbs conjoined together in a single body, wrapped in what looks like a dark grey cloth. At its core, the fusion is comprised of four different shattered Gem Shards that are physically fused together. It possesses four, large eyes. The Clusters' irises and visible Gem Shards are green, yellow, blue, and purple.

"Marble Madness"
The Clusters make a semi-hidden cameo when Peridot is accessing the Facet Five Kindergarten control room.

"Jail Break"
When Peridot and Jasper are at Sapphire's prison cell, Peridot states, "We can't leave yet! The whole point of coming here was to check on the Cluster!".

"Keeping it Together"
The appearance of a Cluster was so horrifying to Garnet that she became unstable to the point where she almost un-fused. Ruby believes the Clusters were created as punishment by Homeworld for The Rebellion. It was eventually 'poofed' by Garnet and currently resides within one of her bubbles in the Burning Room with other broken and corrupted Gems.

Trivia

 * Clusters, along with Rainbow Quartz, have never spoken in the series (not counting the screams emitted by it).
 * Coincidentally or not, if one excludes the Cluster's thumb (which is covered by a boot), it has a glove covering every finger but the middle, while Garnet has a glove covering only her middle finger.
 * The blue "leg" off to the left appears to have the same boots as Amethyst and Ruby.
 * There appears to be no red Gem Shard in the main cluster despite the red leg and arm present in it.
 * The silhouettes of the Cluster members have traits similar to other Gems on the show. For example, their hairstyles are similar in appearance to that of Pearl's haircut from the "Pilot."
 * It should be noted that when the Gems' silhouettes appear, each "body" seems to have a similar body type, and hair style, implying that the attempted forced fusion may have been somewhat successful, before they reformed into a limb-comprised hand.
 * When the Cluster's bubbled gem was sent to the Burning Room, its gem reshaped itself to appear like the Centipeetle Mother's gem.
 * This was later confirmed to be an animation error by Matt Burnett via Twitter.
 * Each of the Cluster's eyes has one plica semilunaris on either side of itself.
 * The Cluster and Garnet's gems share the same placement, both having their gems in the center of their palms.
 * The rock cylinders used to hold the immature Cluster Gems resemble rock core samples.

Cultural References

 * Clusters share many similarities to Frankenstein's monster from the Mary Shelley novel of the same name.
 * Both are made out of body parts of different deceased individuals, acquired via grave robbing.
 * They are unnatural creations which were created through scientific means.
 * Both are represented as tragic, yet horrifying figures.
 * The cylindrical containers may be a reference to the 2012 sci-fi horror movie Prometheus.
 * It may have a reference to one of "The Rotten" arms, from Dark Souls. Since the shape palm is made of hands and legs.

Gemology

 * A cluster of gemstones is a result of gems that fuse together due to extensive pressure from being underground. In most cases clusters are usually fusions of the same gemstone, however, in very rare cases, it is possible for clusters to form from different gemstones.