This is what White Diamond expects of all of us...! From a thin flake of mica to the deepest, hardest stone, we all must make sacrifices for the sake of our perfect empire!
|—Yellow Diamond, "Change Your Mind"|
Before Era 3, the Gem Homeworld maintained a strict Caste System with gemstones having predetermined roles, places, privileges and purposes in the social pyramid, and Gems who deviated from this were considered defective. Since penalties were severe, disgruntled Homeworld Gems kept to themselves or went into hiding. Because there were so many of each Gem-type (except Diamonds), all Gems normally distinguished themselves via serial numbers. The Caste System was divided under the rule of the Diamonds and other Homeworld elites; if Gems were to greet or refer to others in higher sections of the Caste System, they normally prefaced their Gem name with "My" to show they were their superior(s).
The Caste System was somewhat tied to real-world gemology and mineralogy (i.e. Diamonds being the highest as real-life diamond is highest on the Mohs scale of mineral hardness). However, this was not a proper rule for the series as it took creative liberties with Gem-types and their rankings, including but not limited to:
- Ruby and sapphire are varieties of corundum in the real world while Rubies and Sapphires were different and unrelated in the series, possessing different roles in the hierarchy. The same applied to Aquamarines, Emeralds, Bixbites, Morganites and Beryls which were all beryl in the real world but separate and different in the series. Nephrite is under jade in the real world but Nephrites and Jades seem to share no technical relations, although both were voiced by Aparna Nancherla, possibly as a nod to their real-world equivalents.
The Caste System had its beginnings in early Gem history as the Diamonds rose to prominence. When Homeworld's empire officially began, the newly-minted rulers of Homeworld created the system for the purpose of building up their species as the greatest in the universe at any cost. As a result of their places in the hierarchy many Gems either became self-absorbed or self-deprecating depending on where they stood in the Caste System.
There weren't many that dared to challenge this way of life, with those who did being swiftly and permanently silenced. This changed when a Rose Quartz and Pearl suddenly went rogue on a planet called Earth, kickstarting an uprising. Little did anyone else but the Pearl know, her fellow rebel was actually her master Pink Diamond, one of Homeworld's leaders who had become disillusioned upon actually viewing Earth.
After the end of the war, the Caste System continued unopposed despite Gems unknowingly following in Pink Diamond's footsteps; a group of Gems calling themselves the Off Colors caused noticeable trouble outside Homeworld. When Pink Diamond's son Steven Universe revealed himself, he convinced the Diamonds to stand down and give up their tyrannical ways, even personally dismantling the hierarchy and liberating every colony himself.
- Main article: The Great Diamond Authority
Diamonds were the highest-ranking Gems similar to royalty and referred to as the matriarchs of society. They made up The Great Diamond Authority. Most Diamonds are massive, towering over other Gems and most Fusion Gems. They have diamond-shaped pupils in their eyes.
Most Homeworld Gems were fanatically loyal to them and categorized under their respective Diamonds as Blue Diamond once referred to Sapphire as being "of [her] court" and Peridot 5XG said she "was made for" Yellow Diamond. Infidelity displayed towards the Diamonds was considered punishable by shattering at the worst. Their honorific was "My Diamond".
There appeared to be rankings within the Diamonds themselves, as White Diamond was superior to the other Diamonds and the leader of the Authority. Conversely, Pink Diamond was below the other Diamonds and had to obey their orders. However, this relationship resembled more of a dysfunctional family than an actual hierarchy.
Each of the Diamonds had their own aspects of the Empire to govern: White Diamond created the government and held complete control; Yellow Diamond was in charge of the military and Gem production; Blue Diamond oversaw diplomacy and rule enforcement; and Pink Diamond hosted celebrations for accomplishments of the other Diamonds.
Although the Diamonds no longer have control over the Gem race since Era 3, they still acted as the de facto leaders of Homeworld, choosing to help their former subjects instead of hurting them.
Emeralds were high-ranking and diplomatic gems. In The Steven Universe Podcast, Rebecca Sugar and Ian Jones-Quartey emphasized that Emeralds (specifically the one in "Lars of the Stars") were in charge of fleets. The only known Emerald had at least three ships (her personal shuttle, the Sun Incinerator and Destiny Destroyer) and held control over an unspecified amount of Gems.
- Main article: Garnets
Garnets were commanders that aided in conquering and controlling planets; in some cases they were Light Prism-bearers and commanded entire colonies. Certain Garnets seemed to command different types of Gems, but it is unknown if this applied specifically or not. Subtypes included Hessonites, Demantoids and Pyropes.
The Fusion Gem of the same name had no relation as Blue Diamond was surprised to hear she called herself one.
Hessonites are a subtype of Garnets with orange colors who commanded armies and were more focused on strategies and battles.
Demantoids are a subtype of Garnets with yellow-green colors first mentioned by Blue Diamond who served as overseers of the lower and middle classes, worked on colony infrastructures and were more focused on technology.
Pyropes are a subtype of Garnets with pink-red colors first mentioned by Blue Diamond who served as overseers of the upper classes once colonies were completed. Pyropes were noticeably fancier, wearing dresses or gowns and living in places like the Palace of Light.
- Main article: Sapphires
Sapphires were of the nobility class, described as rare and part of the aristocratic elites; in spite of this they had no immunity from outcast status. They could foresee possible events using their future vision and were the only singular Gems with this ability. Their honorific was "Your Clarity". Subtypes included Padparadschas.
Morganites were high-ranking artistic gems in charge of designing architectures. They were ranked high enough to own Pearls and Rubies.
- Main article: Aquamarines
Aquamarines were another type of high-ranking Gems. They appeared to serve as assistants to Diamonds, using their own ships to travel from planet to planet and collect things they wanted. Rebecca Sugar stated that Aquamarines were high-ranked blue Gems.
- Main article: Lapis Lazulis
Lapis Lazulis were valuable to the Empire thus making them high-ranking. As stated by Yellow Diamond they were made for terraforming and as such able to manipulate large quantities of water and utilize it in almost any way imaginable, like slicing even through solid rock and reshaping planets with ease; this was likely how the canyons for Kindergartens were created.
- Main article: Jades
Jades appeared to be high-ranking given the fact that they attended the Era 3 Ball; however it is unknown what their specific roles were. Unlike most Gems they had drastic differences between their physical appearances depending on which type of Jade they were.
Larimars served as ice sculptors for the elites, although it is unclear if this gave them a high ranking or not.
- Main article: Topazes
Topazes seemed to be soldiers, obeying orders and acting as bodyguards; these were traits shared with Quartzes and Rubies. Topazes also acted as guards of places suitable for elite Gems. Rebecca Sugar said Topazes were high-ranked yellow Gems. Although mostly yellow Topazes can come in different colors as well.
- Main article: Nephrites
Nephrites were in charge of piloting spaceships and building colonies. Their ranking was never clearly stated but it could be assumed high enough to captain their own ships but low enough to be ordered around by higher-ranking Gems like Garnets. It should also be worth noting that Yellow Diamond contacted one directly, which she would not do with low-ranking Gems.
Zircons acted as lawyers, though they had no choice over what cases they prosecuted or defended for and were assigned them instead. In the podcast Rebecca Sugar and Ian Jones-Quartey said they had a medium rank, serving the upper classes but with no individual power.
- Main article: Quartzes
Quartzes, like Topazes and Rubies, were soldiers. Made to fit the roles of elite warriors, Quartzes normally had incredible height, broad shoulders, and some even having intimidating muscular builds. Jasper fit this description but Amethyst did not because she "stayed in the ground too long" and was therefore considered "overcooked". Some were used as bodyguards and escorts as shown in Jasper's case. They appeared to be less numerous than Rubies, though greater than Topazes. According to Ian Jones-Quartey, some had defensive powers as well, like Rose Quartzes since "they can't all be tanks". Quartzes were described as being "huge, loyal soldiers". Jasper stated Quartzes were made to fight and her kind specifically always got what they wanted. Some also acted as elite guards at Homeworld outposts such as the Quartzes stationed at Pink Diamond's Zoo or like the Citrines commanded by Emerald and Hessonite. They were Gems common on Earth and the most diverse known Gem-type with subtypes including Agates, Amethysts, Carnelians, Citrines, Jaspers and Rose Quartzes.
Agates are a subtype of Quartzes ranking higher, taking on a much more administrative role as opposed to that of a warrior. Yellow Diamond stated in "What's the Use of Feeling (Blue)?" that they were meant to be terrifying figures intimidating Gems under them into obedience. In "The Trial", it was revealed they could also be bodyguards. It could be assumed based on the way Holly Blue Agate acted around Sapphire that, while having some authority, Agates were not high-ranking compared to Sapphires.
Citrines were a subtype of Quartzes. They appear to have been elite guards serving high-ranking Gems like Emeralds and Hessonites.
Rose Quartzes were new compared to other Gems, having been created on Earth. Sometime between the start of one Rose Quartz's rebellion and Pink Diamond's “shattering” every Rose Quartz in existence was bubbled and was sent to reside inside Pink Diamond's Chamber, at her Zoo. It was stated in "That Will Be All" that Blue Diamond wished to keep them around for the sake of preserving Pink Diamond's legacy, while Yellow Diamond wanted them shattered as they believed one to be responsible for the start of the Rebellion and Pink Diamond's destruction. However, this was not truly the case. In actuality, the Rose Quartz who created the rebellion was actually Pink Diamond in disguise, wishing to preserve life on the planet and faking her shattering in order to do so. While still being soldiers, Rose Quartzes were known more for their defensive powers rather than the offensive abilities other Quartzes had, although this may be exclusive to the Rose Quartz who was Pink Diamond and not the cut of Gem as a whole. Their gemstones appeared to be modeled after the table facet of Pink Diamond's gemstone, lacking the pavilion and having a mirrored back. It is most likely that their sole reason for being created was to keep Pink Diamond’s identity a secret from both Homeworld and the Crystal Gems.
Cherry Quartzes are a subtype of Quartzes with pink coloring. Based on other Quartzes, it could be assumed they were soldiers as well.
Amethysts are a subtype of Quartzes mostly with purple coloring. The Prime Kindergarten on Earth specifically produced Gems of this type, including the Crystal Gems’. Amethysts, just like every other average Quartz Gem, acted as soldiers and/or guards, as seen with the Amethysts guarding Pink Diamond's Zoo.
Carnelians are a subtype of Quartzes with maroon-red coloring. The Beta Kindergarten on Earth produced Gems of this type. Based on other Quartzes, it could be assumed they were also soldiers.
Jaspers are a subtype of Quartzes mostly shown to have tangerine skin and red-orange markings, but can come in different colors depending on the type of Jasper they were. Similar to other Quartzes below Agates, they acted as either soldiers or guards. Known subtypes include Ocean Jaspers, Biggs Jaspers, and Zebra Jaspers.
Tiger's Eyes are a subtype of Quartzes yet to be seen but mentioned by name.
Angel Aura Quartzes
Angel Aura Quartzes are a subtype of Quartzes with iridescent coloring. Based on other Quartzes, it could be assumed they were soldiers as well.
Cherts are a subtype of Quartzes with brown and beige coloring.
Flints are a subtype of Quartzes with gray-blue coloring.
- Main article: Peridots
Peridots served as technicians and engineers, sometimes performing field assignments on other planets. Being workers, they had a low ranking and were only allowed into elite Homeworld areas if a job was needed to be done there.
In Era 2, Peridots and even other Gems were given tools such as Limb Enhancers to compensate for a lack of strength and unique abilities due to the depletion of resources on Homeworld. Despite this Peridot 5XG was shown to have ferrokinetic abilities, implying Peridots and other Gems created after Era 2 were more powerful than initially believed.
- Main article: Bismuths
Bismuths were builders for aristocratic members of society. As such, they possessed a broad stature for intense physical labor, above-average resistance to heat and damage and hands capable of fluidly changing form without the need for typical shapeshifting to fit a wide variety of purposes. Their tend to be very colorful in terms of hair and gemstone color, but mostly came in cool colors in terms of skin tone.
Obsidians are tall Gems with a muscular upper half. Like Bismuths, they were workers who dug trenches and other encampments for Homeworld’s armies; certain subtypes seemingly worked in specific areas. Unlike Garnets, who shared physical similarities regardless of being Fusion Gems or not, the only one seen shared no physical characteristics with the Fusion Gem of the same base name. Subtypes included Snowflake Obsidians.
- Main article: Rubies
Rubies were another type of soldiers and were one of the lowest-ranked Gems in Homeworld’s caste system. They also filled the roles of escorts and bodyguards for elite Gems, such as Sapphires. They also functioned as scouts. Due to the abundance of Ruby Gems in the empire, they were considered expendable footsoldiers or cannon fodder and much of their worth came from fusing with each other. Rubies had almost no differences in appearance, mostly being red and having square-shaped afros, and were not supposed to have different personalities; the fact they did "flies under the radar" because they acted seriously around high-ranking Gems.
Spinels were entertainers and court jesters. They were implied to be rare, as it was stated in "system/BOOT.pearl_final(3).Info" that Steven was a "lucky one" for acquiring such a Gem. The body of the only one seen was elastic and malleable compared to other Gems, even Bismuths. According to Rebecca Sugar, if more Spinels had been shown their gems would have been shaped like playing card suits. This may have been a joke referring to the fact that both hearts and diamonds are playing card suits.
- Main article: Pearls
Pearls were servants and had such a low rank, they were not even considered real Gems, but viewed as property. They were expected only to serve and be submissive and obedient, simply waiting on their owners until being told "that will be all" and not acting independently in any way. Pearls also provided simple luxuries like singing, dancing, and entertainment by projecting holograms. Unlike other Gems, Pearls did not have a set uniform, instead their colors, outfits and even the position of their gemstone was made customizable to resemble the Gem they were serving. However, if the owner wished a Pearl could emerge with default settings just like the Crystal Gem Pearl. Unlike other Gems, Pearls were not created in Kindergartens, but made in a facility called the Reef, where they could also be customized, repaired or rejuvenated if necessary.
- Main article: Pebbles
Pebbles also acted as servants, but unlike Pearls who belonged to individual Gems, they appeared to serve everyone. They had building and sewing skills that were enough to fulfill different tasks at incredible speed. They were mainly used to create furniture and decorations in living quarters while staying out of sight. They appeared to be the lowest-ranking Gems as they were seldom acknowledged or thanked.
Gems with unknown types and societal roles. These types of Gems have been seen in full but their places in the system have not alluded to enough to determine their exact positions.
Bixbites are slim, red and yellow gems with singular eyes. Their ranking is unknown, but it was implied their role involved being able to cut with exact precision. It is possible they worked in construction and manufacturing.
Rutiles are tall, lanky red Gems with a somewhat rectangular build resembling real-life rutile. Although not much was known about them they seemed to have piloting capabilities. Judging by the words of the Rutile Twins, they appeared to be mass-produced thus likely holding a low rank, although this is unconfirmed.
Spodumenes are towering, sinuous gems with large singular eyes occasionally covered by something resembling hair. Subtypes include Orange Spodumenes.
Tourmalines are round Gems with balloon-like features. Only a fusion of two Tourmalines has been seen.
Miniature Green Gem Type
This type of Gem belongs to the Heaven and Earth Beetles. It has varying shades ranging from bright lime yellow to pale forest green. They are small in stature even compared to Aquamarines and appeared to have been high-ranked given they had spires to live in.
Stocky Violet Gem Type
Very little is known about this type of Gem. They appear to have a hunched, stout build and the only instance shown possesses corruption scars in the form of a gelatinous cloak similar to Spodumenes, revealing very little about her physical features.
Large Green Gem Type
Not much is known about this type of Gem although one has a gemstone similar to the Heaven and Earth Beetles.
Other Unknown Gem-Types
- Glasses - The only one seen was a subtype named Desert Glass, whose gemstone was embedded in a pillow. Even though she was trapped and presumably corrupted, she had the ability to create structures out of sand.
- Chrysocollas - Blue Gems with the ability to "slink" from one place to another.
- Chalcedonies - Gems that can drill into rocks and other minerals. The only one seen was a subtype called Blue Chalcedony.
- Albites - The only one seen had her gemstone embedded in an Obelisk, powering it and by extension the death traps in the Pyramid Temple.
- Moonstones - Gems that can turn their physical forms invisible, except for their gemstones.
- Grossular Diopsides/Titanites - Purple Gems that can dig underground and create burrows.
- Beryls - Nothing is known about this type of Gem, aside from the fact that one was a Crystal Gem and later corrupted. Despite sharing a real-world mineral class with Aquamarines, Emeralds, Bixbites and Morganites they appear to be unrelated.
- Serpentines - Nothing is known about this type of Gem, aside from the fact one was a Crystal Gem and later corrupted.
- Pyrites - Blue Diamond mentioned she let Pink Diamond name a batch Fool's Gold. They may be very high-ranking, due to a small batch seemingly being regarded as a specialty by White Diamond, of all Gems.
- Comby - A Gem in the shape of a comb who served Blue Diamond by singing to her and being used as a literal comb. It is unknown what Gem she is, but she resembles the Pebbles and is, presumably, one herself.
- Sentient Walls - Gems in the form of mobile walls in the hallway of Yellow Diamond's Extraction Chamber.
- Sentient Statues - Presumably-harvested Gems appearing in Blue Diamond's Extraction Chamber. Their full physical forms have not been seen.
- Kyanites - Blue Diamond mentioned she let Pink Diamond bring alien worms to Homeworld from a colony of them.
- Micas - A type of Gem only mentioned.
- Chalks - A type of Gem only mentioned.
- Main article: Fusion Gems
Fusion Gems, specifically Same-Gem Fusions were used as weapons, especially in times of war. Fusions outside of battle were considered and regarded as inappropriate, unorthodox, disgusting, embarrassing or discomforting to behold. However, it was revealed Fusions found outside of battle were indeed legal on Homeworld, provided they were of the Same-Gem type and could only be allowed for certain positions (e.g. soldiers); even then they were looked down upon for a capacity of sentimentality.
Although fusions of the same type were seen as acceptable, such as Fusions consisting of Rubies and Topazes, fusions between Gems of different varieties were considered abnormalities as Blue Diamond's court referred to Garnet, a Cross-Gem Fusion between a Ruby and her Sapphire as "disgusting" and "unheard of". Other examples include Rhodonite and Fluorite, two Cross-Gem Fusions that were forced to hide to avoid being shattered. The reasoning for this prejudice was because they created entirely new Gems which disrupted Homeworld's society; the new Gems could have had no place in the Caste System and thus hold no job beneficial to Homeworld.
Defective Gems, also known as Off-Colors served no use to the Empire, were thus cast out of its society and if caught were shattered. The only exceptions were the Earthmade Quartzes kept in service by Blue Diamond; Amethyst was another exception provided she wore Limb Enhancers like Era 2 Gems to reach her "height requirement".
- Main article: Corrupted Gems
Corrupted Gems, also known as Gem Monsters became corrupted by the Diamonds assuming monstrous and nigh-incoherent forms. One of the main objectives of the Crystal Gems other than the protection of humanity and Earth was to defeat, contain and hopefully cure these Gems. They did not exist on Homeworld and as such had no place in its society.
- Main article: Gem Shards
Gem Shards or Shards are deceased Gems shattered for being defective or rebelling. However, some can still hold "a powerful partial consciousness that has been harnessed by Gems throughout history to create semi-sentient drone soldiers with the capacity to follow basic orders"; like intact gemstones they could be used as power sources. Unfortunately, this proved dangerous to the point Shards in containers ended up attacking everything around them; in some cases they regenerated as disembodied limbs that would seek out the missing parts of themselves in hopes of reuniting.
Cluster Gems, otherwise known as Forced Fusions or Gem Mutants were shattered Gems fused against their will into monsters similar to Corrupted Gems. The Cluster was a result of the Diamonds attempting to harness this process to create a "geo-weapon" which would destroy Earth and other planets as well, but the Gems in the Cluster bubbled themselves before they could any harm and rested peacefully in the planet’s core. Yellow Diamond was their creator, and since the dawn of Era 3 has made it her goal to fix and revive the Gems used in her experiments, including the Cluster.
- This utilitarianism and/or functionalism-based judgement of an individual's worth on their outward appearance was similar to the Caste System/Functionism from Transformers, specifically the franchise's more recent entries in that they were glaringly suppressive, toxic, flawed and resulted in uprisings that brought about the end of a time during which many lived in fear for their lives should they have stepped out of line.
- The movie introduced Gem Rejuvenators which were used to wipe the memories of disobedient Gems, making them act and look the way they did when after emerging. However, due to being able to restore their memories from something that influenced them, this process was retired in favor of imprisonment, harvesting and shattering.
- The Steven Universe Podcast MiniRecaps: Lars of the Stars (ep. 7)
- Rebecca Sugar in Crewniverse Reddit AMA
Q: "Are Lapis Lazulis high ranking gems?"
A: "Lapis Lazulis are extremely valuable to the Gem Empire."
- The Steven Universe Podcast Homeworld Gems - Rebecca Sugar, Ian Jones-Quartey, Erica Luttrell, Joe Johnston, and Hilary Florido (Vol.2/Ep.8)
- Ian Jones-Quartey's tweets on Rose
- Rebecca Sugar in 
Q: "So...with this whole ball thing. We've seen that Gems do know what music is, and what singing is. So why didn't Peridot know what singing is?"
A: "She would never have been in the palace unless she was there for a job. She's essentially a maintenance worker."