"Gems" are an extraterrestrial species of magical beings that play a key role in Steven Universe. Their origins, history, and culture are not well understood, although numerous small hints throughout the series imply that Gems are an interstellar race which at one point maintained several outposts on Earth, but suddenly fled and left many of their artifacts to ruin, with the only Gems currently on Earth being what is left of the Crystal Gems, the corrupted Gem Monsters, along with a small group of stranded Gems from the Gem Homeworld.
Gems are characterized by the gemstone embedded somewhere on their body, which seems to be analogous to a brain or CPU.
Gems' physical forms are projections from their gemstone, and Gems have the ability to customize their physical forms, which are made of hard light, at will, with their only constant feature being their gemstone and color scheme (shapeshifting is not permanent and Gems will return to their "default" form eventually). Although the species has no sexual dimorphism, Gems' physical forms typically have characteristics associated with human femininity. Because of this, all Gems are inherently sexless, with the sole exception being Steven, due to his half human parentage.
Gems have many capabilities, which can vary from Gem to Gem, including weapon-summoning, fusion, the power to 'store' material in their gemstones, and bubble creation. Note that some Gems, such as Lapis Lazuli, are not able to summon a personal weapon. All Gems with their own weapon have the ability to direct energy through their weapons, such as Garnet using her gauntlets to charge Greg's van, Pearl firing an energy blast from the tip of her spear, and Amethyst sending bursts of energy through her whips.
Gems cannot die by any natural cause, and do not have to eat and sleep to survive. They, however, can still eat and sleep if they so desire. The only way to permanently destroy or "kill" a Gem is to destroy their gemstone. When the physical body of a Gem is seriously injured, they will retreat into their gemstone to regenerate. Regeneration is special in that Gems can make permanent changes to their physical form while regenerating. The length of the regeneration process can range from minutes to weeks, but a "rushed" regeneration can suffer from physical deformities. Regeneration can be prevented if a gemstone is bubbled or otherwise constricted, such as within a mirror or a pillow.
If a Gem's gemstone is damaged, their physical form will deteriorate and "glitch" and they are unable to properly use their powers as well as their language. It is also worth noting that a Gem's gemstone can be used as an energy source, even if damaged. Gem Shards, the remnants of a shattered gemstone, possess a "powerful partial consciousness" which can grant sentience to their containers and have been used to create drone soldiers. Gem Shards have also been forced to fuse together over time to form a Cluster Gem.
- There are two known groups of Gems: Homeworld Gems and Crystal Gems.
- The Homeworld Gems are Gems currently living on the Gem Homeworld. Historically, Homeworld Gems wished to exploit Earth and established a foothold on the planet, by which they used to create new Gems, known as a Kindergarten. The Homeworld Gems, including Peridot, Jasper, Lapis Lazuli and their currently unseen superior known as Yellow Diamond, are a hostile military force that invades planets, bleeds their natural resources dry, and "leaves them for dead."
- The Crystal Gems are a group of rebels who chose to join Rose Quartz in the fight against Homeworld in order to defend Earth. The only Crystal Gems that remain are Garnet (the fusion of Ruby and Sapphire), Amethyst, Pearl, and Steven Universe, the son of Rose Quartz.
- Over five thousand years prior to the start of the series, Rose Quartz organized the Crystal Gems to oppose the Homeworld Gems. The Crystal Gems won, as stated by Pearl in "Rose's Scabbard", and the Homeworld Gems were driven from Earth, leaving behind many relics and temples.
- Gem civilization is very advanced, capable of creating spaceships, pocket dimensions, and teleporters.
- Gem culture is quite different from human culture, given the Crystal Gems' confusion over seemingly everyday human cultural practices, such as birthdays and video games.
- The Gem culture is an ancient one, predating all known human civilizations.
- Gems have their own written language, which is inscribed on many of their temples, as first seen in Steven's Room in the "Pilot".
- Gem architecture can be seen scattered across the Earth in the form of the structures, such as the Lunar Spire, the Communication Hub and the Galaxy Warp.
- While there has never been mention of Gems practicing any form of spiritualism, the existence of the Moon Goddess Statue, along with the Sea Shrine and the Pyramid Temple, imply some sort of belief system.
- While Gems are incapable of reproduction, romantic relationships do exist in their society, such as that of Ruby and Sapphire.
- Gem culture does not have a gender binary or a concept of gender.
- Gems refer to each other using feminine pronouns, but have no particular reason for doing so beyond arbitrary convenience.
- In their default state, Gems typically appear feminine by human standards, and they can use their shapeshifting abilities to deliberately assume overtly gendered forms.
- Being half human, Steven possesses the characteristics of a male human individual.
The Gem Homeworld maintains a strict caste system based on gemstone. In "Back to the Barn", Peridot describes how Pearls are created to be servants and meant to be completely subservient to their owners, and the rarity of a Peridot owning a Pearl. In Guide to the Crystal Gems, each Gem has a type.
- Quartz - The Prime Kindergarten created Gems of the Quartz variety, as revealed in Guide to the Crystal Gems. They are supposed to be huge, loyal soldiers who are broad shouldered, and intimidating.
- Pearls - In "Back to the Barn", Peridot stated that Pearls are an accessory and a made-to-order servant who are just there for standing around, looking nice, taking orders, and holding other Gems' stuff. It is implied that there are varying qualities, and that Pearl is an especially fancy one.
- Pearl - An independent Pearl who breaks the rules of what a Pearl is supposed to be.
- Peridots - Peridots are implied to be technicians and have a higher rank than Pearls.
- Peridot - The only known Peridot in the series who is a certified 'kindergartener' and technician.
In the short "How are Gems made" It's explained that Gems "aren't born, they're made when some Gems from outer space came here with these big machines! They put the machines on Earth and shot this junk into the ground, and then boom, you pop right out!". In addition it's revealed that Gems are formed fully developed "being a weak baby would be a pain, so, they suck up all the good stuff from the ground so we pop out all big and strong".
In "On the Run", it is revealed that the Homeworld Gems invaded Earth several thousand years ago and used Kindergarten to create new Gems using the method described in "How are Gems made"; and that Amethyst was one such Gem. This process was very harmful to the environment to the point where, if it were allowed to continue, it would lead to "the destruction of all life on Earth", according to Pearl in "Marble Madness". Amethyst refers to all the Gems created through the process, herself included, as "parasites".
While biological reproduction is an alien concept to Gems, it is not impossible for them; while Gems can't reproduce with each other they can create Gem-hybrid offspring. Through shape-shifting, they can perfectly replicate reproductive organs of organic beings for their "human constructs" in order to reproduce. Rose Quartz is the only Gem to have done this and her son, Steven, inherited her Gemstone, without which she could not project a physical form and subsequently "died". In "Guide to the Crystal Gems" it is implied that Gems are capable of reproducing without having to give up their physical forms.
- Fusions are capable of further fusing with Gems, as exhibited in "Coach Steven" (in which Garnet fuses with Amethyst).
- Fusions tend to highly exaggerate whatever personality traits are shared amongst the majority of the Gems comprising the Fusion. Sugilite seems to inherit her impulsive and irrational behavior from Ruby and Amethyst, while Sardonyx seems to get her haughty and self-absorbed personality from Sapphire and Pearl.
- When Gems in a given Fusion have incompatible personalities, or have conflicting motives for fusing, and for whatever reason do not (or can not) terminate the Fusion, it results in an Unstable Fusion. When this happens, the constituent Gems risk losing touch with their individual personalities the longer the Fusion persists.
- In "Coach Steven", Sugilite is the first example of Gems remaining as an unstable Fusion for too long. It can be surmised that this case arose because Ruby and Amethyst have many similarities in personality, while Sapphire's personality strongly contrasts with both. Sapphire's presence was enough to cause instability, but not enough to "outvote" Ruby and Amethyst and cancel the Fusion.
- Malachite is another example. At the end of "Jail Break", Jasper is clearly trying to escape the Fusion. Either Jasper has very low willpower (not unlikely, considering her barbaric personality), or Lapis Lazuli has a great deal of mental fortitude, or a combination of both.
- The majority of known Gem weapons are medieval: Garnet's gauntlets, Pearl's spear, Amethyst's whip, Steven/Rose's shield, Opal's longbow, Sugilite's flail, Jasper's crash-helmet, Ruby's gauntlet, and Sardonyx's war hammer.
- The process for each Gem to summon their weapons depends on a different state of mind for each of them.
- Amethyst places little effort or concentration, claiming that it "just happens" when she needs to summon her weapon.
- Pearl claims that her process as being perfect and calculated, using the science of a flower petal dancing in the wind to describe how hard work and dedication can help master the properties of one's own gemstone and "perform their own dance".
- Garnet claims that she summons her gauntlets by linking her mind with the energy of all existing matter, channeling the collective power of the universe through her gem(s), matching her calm and meditative temperament.
- Steven's means of summoning his shield is still unknown, though it is thought to be caused when he experiences pure joy, having first activated his gem after taking a bite of his favorite ice-cream sandwich, his ability to summon his weapon can also be attributed to the feelings of love and the desire to protect.
- Say Uncle reveals that Steven's powers are maternal, and that he summons his shield to protect the things he cares about. Though the episode is considered non-canon, the description of how Steven summons his shield seems to be accurate.
- Ian Jones-Quartey has stated that Steven is the first Gem to use masculine pronouns.
- Rebecca Sugar and Ian Jones-Quartey have stated that Gems use feminine pronouns by default.
- Although Gems are genderless, in their human-like forms they are anatomically constructed similarly to human women, and referred to by the pronouns used by human women.
- This is demonstrated in "Ocean Gem", as Pearl called Lapis "she."
- Pearl also referred to Rose Quartz as "she", while reminiscing in "Rose's Scabbard".
- Garnet, Pearl, and Steven referred to Peridot as "she".
- Garnet referred to Jasper as "she".
- Gemstones can be used as a power source, even if damaged.
- In Chille Tid, Gems are shown to be able to sleep and dream like humans, though like eating they do not require sleep in order to function. However it is also shown that Gems can tire physically when exhausted.
- Gem's physical bodies are capable of producing bodily fluids, and in "Coach Steven", Pearl can be observed to have scrapes on her "skin".
- Pearl referred to their bodies as "human construct(s)" in "Fusion Cuisine".
- Ian Jones-Quartey has stated that Gems do possess DNA, and that Rose Quartz was able to pass her traits on to Steven, although this would contradict Pearl's implication that Gems are inorganic in Alone Together.
- Gem-hybrids can fuse with humans, such as Steven did with Connie to form Stevonnie, but it's unknown if hybrids can fuse with Gems.
- Gems cannot fuse with humans, as shown in "We Need to Talk".
- There can be multiple Gems of the same type.
In "The Return", "Friend Ship" and "Back to the Barn", Jasper, Peridot, and Pearl herself have referred to her as "a Pearl", implying there are more.
- In When It Rains, Peridot assumes that Steven is "some kind of Quartz" from an Earth's kindergarten.
- In Guide to the Crystal Gems, Steven, Amethyst, Rose and Jasper all have their Gem type listed as Quartz.
- Peridot states in "Back to the Barn" that Pearls are mass-produced as a subservient race, and implies that Peridots are used as technicians.
- It is unknown if the placement and shape of a gemstone is a choice, or a default.
- Gems' skin tones are always related to the color of their gemstones, however they don't always match precisely, for example Rose Quartz's skin tone has a lighter, peachier shade than her gemstone.
- In the comic series, Pearl has been shown to absorb objects into her gem and has gotten sick when she absorbed too many objects into her gem. It is unclear whether other Gems can do this.
- This ability may be inherent to Pearls specifically, as it would account for Peridot's comments about Pearls being made to hold things.
- Although, in "Serious Steven", Garnet appears to be storing the temple key in her gems since she had to summon it as she wasn't carrying it with her prior to arriving at the Gem Battlefield.
- It is implied that Gems either don't need to breathe, can hold their breath for long periods of time, or breathe differently from humans.
- In "Nightmare Hospital", it is revealed Gems do not have a heart or heartbeat.
- While Gems do not require sustenance, it is implied in "Catch and Release" that they produce bodily waste after consuming food.
- Many aspects of Gem culture are similar to the Gallifreyans of Doctor Who fame.
- Both societies predate human, both species are capable of regenerating themselves (though Gallifreyans are less predictable), and are typically dismissive of humanity.