Caste System

Homeworld maintains a strict caste system, with each type of gemstone having a predetermined role and place in the social pyramid, each with their privileges and ordained purposes. Any Gem who, in any way, digresses from their role, be it intentional or not, would be considered defective. Since the penalties for such actions are severe, most disgruntled Homeworld Gems either keep their dissension to themselves or are forced to go into hiding. Because there are so many of one type of Gem, the Homeworld Gems — except the Diamonds — distinguish themselves via coded serial numbers. So far the known castes are:

Diamonds
Diamonds are the highest caste, similar to royalty and referred to as the "matriarchs" of Gem society; they make up The Great Diamond Authority. All Homeworld Gems are fanatically loyal to the diamonds, seeing as Peridot formerly adored Yellow Diamond. Gems also appear to be categorized under their respective Diamonds, as Blue Diamond referred to Sapphire as being "of her court" and Peridot saying she was "made" for Yellow Diamond. They are also of a massive size, towering over the other types of Gems seen, even some fusions. Any form of infidelity displayed towards the Diamonds is considered punishable by death. Their honorific (from their subordinates) is "my Diamond".

Sapphires
Sapphires are of the nobility class, described as being rare aristocratic gems and part of the "Elite". They can see into the future using their "future vision". So far, Sapphires are the only non-fusion gem type shown with this ability. However, defective Sapphires like Padparadscha are only able to have visions of events slightly in the past. Their honorific is "your clarity".

Agates
So far, Holly Blue Agate is the only Agate shown in the show. She is in charge of a group of Quartz soldiers and manages Pink Diamond's Zoo. Quartzes of her type seem to have a higher ranking than standard "made-for-battle" ones. Their purpose seems to be administrative in nature. Yellow Diamond states in "What's the Use of Feeling (Blue)?" that they are meant to be terrifying figures that intimidate Gems under them into obedience. In "The Trial", it is revealed that they can also be bodyguards for high-ranking Gems, such as a Diamond.

Morganites
While the exact role of a Morganite is unknown, they are known to be in charge of lower-ranking Gems. One Morganite is mentioned by Rhodonite to have, at some point, replaced and outcasted Rhodonite's components after discovering they liked to fuse.

Aquamarines
According to Pearl (as well as Aquamarine's own gloating), Aquamarines seem to have a high rank in Homeworld's hierarchy. Rebecca Sugar says that Aquamarines are one of the very high-ranked blue Gems on Homeworld.

The only Aquamarine seen was the one sent to Earth by the Diamonds to retrieve different "variations" of humans for Pink Diamond's Zoo. Aquamarine is the smallest non-Corrupted Gem seen so far.

Lapis Lazulis
Lapis Lazulis were made to terraform, as stated by Yellow Diamond. Peridot states that Lapis Lazulis are typically partial to water and flying. It is unclear how high they rank in the caste system, though they seem at least equal to or higher than Peridots.

Lapis Lazulis' use of terraforming planets likely explains Lapis Lazuli's ability to manipulate massive bodies of water with ease (and possibly explaining her enjoying farming).

Bismuths
Bismuths are a building caste, in charge of constructing temples, spires, arenas and other structures for the aristocratic members of Gem society on both Homeworld and Gem colonies. As such, they possess a broad stature for intensive physical labor, above average resistance to heat and damage, and hands capable of fluidly changing form, without the need for typical Gem shapeshifting, to fit a wide variety of purposes.

Unknown Green Gem
Currently, the Centipeetle's Gem type is unknown. However, her role in Gem society is shown in "Monster Reunion". These green Gems travel in large groups, flying on Gem spaceships and landing on Gem colonies. Once they arrive, they begin development and build structures on the planet.

Nephrites
Not much is known about Nephrites in the caste, but they have been mentioned to pilot Gem Ships. One Nephrite pilot was mentioned to have been fought by Pearl.

Peridots
Peridots serve mainly as technicians and Kindergarteners, sometimes performing field assignments on other planets, such as the Peridot who befriends Steven. Their exact role is currently unknown; however, they are higher than Pearls (but not high enough to own a Pearl of their own). Era 2 Peridots are given Limb Enhancers to compensate for their lack of abilities older gems have, due to the depletion of resources on Homeworld. One Peridot, so far, has been shown to have telekinetic capabilities over metallic objects.

Topazes
Topazes' roles seem to be that of soldiers, obeying orders and acting as bodyguards for their assigned Gem. A fusion of two Topazes was sent to Earth by the Diamonds to retrieve different "variations" of humans for Pink Diamond's Zoo. These two Topazes are incredibly efficient at trapping and engulfing victims within their fusion. Topaz is especially proficient at this. Rebecca Sugar says that Topazes are very high-ranking Yellow Gems. However, they are not as highly ranked as Aquamarines.

Quartzes
Quartzes are a soldier caste. Made to fit the role of an elite warrior, Quartzes have incredible height, broad shoulders, and an intimidating muscular build. Rose Quartz and Jasper both fit this description. Amethyst is also a Quartz, although she does not fit the description because she "stayed in the ground too long", and was, therefore, overcooked. Some Quartzes are used as bodyguards and escorts, as shown by Jasper. They appear to be less numerous than Rubies. According to Ian Jones-Quartey, some have defensive powers as well (like Rose's) since "they can't all be tanks". Quartzes were described to be "huge, loyal soldiers". Jasper states that Quartzes are made to fight and that Jaspers, specifically, always get what they want. Some Quartzes also act as guards at Homeworld outposts, such as Pink Diamond's Zoo. Quartz is the largest known Gem type with Gems including Amethysts, Carnelians, Jaspers, and Rose Quartzes.

Zircons
Zircons act as lawyers for the courts of the Gem Homeworld. Presumably, they have no choice over what cases they prosecute for or defend (as revealed in "The Trial") and they are assigned cases instead.

Rutiles
Rutiles' roles in Homeworld's caste system are unknown. The only Rutiles shown so far are the Rutile Twins, a defective pair of Rutiles who merged together when first forming, making them permanently conjoined as one Gem.

Rubies
Rubies are another type of soldier caste. Garnet describes them as "common", seeing as they are all originally identical to one another. They appear to be used as personal escorts and bodyguards for high-ranking Gems. Seeing as they are so numerous, inferred from Ruby's comment of there being "tons" of her, Rubies are considered somewhat unimportant and highly expendable grunts, though they compensate by fusing together into bigger constructs of themselves. Rubies are also sent to different planets to seek out specific Gems. As Rubies are merely common soldiers, they are not very intelligent, being easily fooled by Steven's claims that Jasper is on Neptune and Amethyst's obvious disguise as Jasper, and according to Holly Blue Agate, they are seen as being incompetent or irresponsible.

Pearls
Pearls are servants in the caste. Described by Peridot as being "someone's shiny toy", Pearls serve as domestics and ladies-in-waiting to their owners. They are expected only to serve and be submissive and obedient. Their work consists of domestic tasks such as cleaning or holding their owners' things. Pearls are also status symbols on Homeworld reserved for higher castes, as Peridot comments that the idea of a Peridot owning a pearl is a ridiculous notion. Pearls may also be earned by committing an act of heroism towards the Diamonds, as Eyeball states in "Bubbled". As seen in "Gem Heist", Pearls also serve the function of footmen, opening doors for their masters; they are expected to consistently exhibit subservience by remaining silent unless spoken to and remaining a few paces behind their superior when walking with them. They also provide simple luxuries like singing, as seen in "That Will Be All". Physically, all Pearls appear to have a slender form and a beak-like nose. They can also be "customized" to resemble their owners in color, appearance, and Gem placement, (as seen from Yellow and Blue Pearl). However, this is not always the case, as Pearl successfully passed off being Sapphire's Pearl despite sharing no resemblance to her "owner".

Fusions
Fusions (or specifically Same-Gem Fusion) are used as weapons in the caste. They are used in times of war, seen as objects rather than their own beings. A fusion outside of battle is considered highly inappropriate and extremely unorthodox, being regarded as disgusting, embarrassing or discomforting to behold (as inferred from Jasper and Peridot's reactions towards Garnet). However, the existence of Topaz reveals that, despite Peridots and Jaspers prejudice, fusion outside of battle is indeed legal on Homeworld providing the fusion is same-gem and may only be allowed for certain Gem castes (e.g. soldiers).

To a further extent, only fusions of the same type are seen as acceptable (such as a fusion consisting of several Rubies or several Topazes). Fusion between Gems of different varieties is considered more of an abnormality in Gem society, as the Gem diplomats of Blue Diamond's Court in "The Answer" refer to Garnet's fusion as "disgusting" and "unheard of". As another example, Rhodonite and Fluorite, two "off color" fusions of different Gem types, were cast out from Homeworld's society and forced to hide to avoid being shattered. Rhodonite's components were replaced by her commander, Morganite, after she found out that they liked to fuse.

Rose Quartzes
Some time between the start of Rose Quartz's rebellion and Pink Diamond's shattering, every Rose Quartz in existence was bubbled, with the only exceptions being Steven and his mom. They currently all reside in the Rose Quartz Bubble Room in Pink Diamond's Zoo. While Blue Diamond only wishes to keep the Rose Quartzes around for the sake of preserving Pink Diamond's legacy, Yellow Diamond wishes that every Rose Quartz be shattered because one of them started the rebellion and shattered Pink Diamond. While being Quartz soldiers, Rose Quartzes are known for their defensive powers rather than the average offensive abilities Quartzes have.

Defective Gems
Gems that are defective (or those referred to as "off color") serve no use to the Gem empire and are outcasted from society. If caught, off colored Gems are shattered.