Gems

"Gems" are an extra-terrestrial species of magical beings that play a central role in "Steven Universe". Their origins, history, and culture are at this point not well understood, although numerous small hints throughout the series imply the 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 still on Earth being the Crystal Gems.

Regular Gems

 * Pearl
 * Amethyst
 * Lapis Lazuli
 * Rose Quartz
 * Peridot
 * Sapphire
 * Ruby
 * Jasper
 * Yellow Diamond

Gem Fusions

 * Garnet
 * Opal
 * Sugilite
 * Alexandrite
 * Malachite

Half-Gems

 * Steven

Quarter-Gem Fusions

 * Stevonnie

Description
Gems are characterized by the gemstone which every Gem has embedded somewhere on their body. Each Gem shown thus far is unique and the Gemstone seem to be analogous to the brain or a CPU. Gems generally take on the form of feminine humanoids, but appearance varies from Gem to Gem with their colors palettes mirroring the color palettes of their gemstone (e.g. Garnet is mainly red, Amethyst is mainly purple/violet) and gems have the ability to change their physical forms (which appear to be some sort of hard-light construct) at will with their only constant feature being their gemstone (which will manifest on any form they take) and palette. Because of this, all Gems are inherently sexless and while the species lacks sexual dimorphism, they choose to manifest with feminine physical forms with the only exception thus far being Steven, due to his half human parentage.

Gems have numerous other abilities such as summoning weapons through their gemstones (although this may not be universal as Lapis Lazuli and Peridot have not yet been observed to have weapons), the ability to fuse with each other to create more powerful Gems such as Opal and Sugilite, and the power to 'store' material in their gemstones (not counting their weapons) such as the mirror containing Lapis Lazuli from "Ocean Gem" and the police tape from "Lars and the Cool Kids", both of which Pearl withdrew from her gem. All Gems seem to have the ability to harness and transfer energy through their weapons, such as Garnet using her gauntlets to charge Greg's van in "The Message", Pearl firing an energy blast from the tip of her spear in "Watermelon Steven", and Amethyst sending a burst of energy through her whip in "On the Run". On top of this Individual Gems may have specialized abilities as well, such as Garnet's abilities to swim in lava and see into the future, or Lapis Lazuli's ability to manipulate water, and Pearl's ability to manipulate sand.

"So Many Birthdays" revealed that Gems are functionally immortal and cannot die from aging or food  poisoning, although Gems can still be killed if their Gemstone is destroyed. It has also been revealed in"  Steven the Sword Fighter "  that when a  Gems' physical body is badly injured, they will retreat into their gemstone to regenerate (this process can take weeks or longer). It seems that when a gem is bubbled it prevents regeneration from taking place.

In " An Indirect Kiss " it was shown that if their gemstone is damaged, their body may go through glitch like deformities. It is also noteworthy that a Gems' gemstones can be used as a power source even if it's damaged, as in the case of Lapis Lazuli, whose cracked gem was used to power a magic mirror that could record and show the past, but she was unable to escape or manifest a physical form, with her only means of communication being through the mirror.

Similar to this are Gem Shards which appear to be the remnants  of a shattered gemstone and, as described by Pearl, were used by other Gems to create "drones" and could grant rudimentary sentience to their containers.

Culture

 * There are currently two known groups of Gems: The Homeworld Gems and the Crystal Gems.
 * The Gem Homeworld wished to exploit Earth and established a foothold on the planet by which they used to create new Gems, known as Kindergarten. The "Homeworld Gems" whose agents include Peridot, Jasper, Lapis Lazuli, and their currently unseen superior known as Yellow Diamond.
 * The Crystal Gems are made up of exiles from the larger Gem Empire ruled by its Homeworld, after they chose to join Rose Quartz, in rebelling against the Homeworld in order to defend the Earth. The only Crystal Gems that remain are Garnet, Amethyst, Pearl, and Steven, whose mother was Rose Quartz.
 * Over five thousand years before the start of the series, Rose Quartz organized the Crystal Gems to oppose the Gem Homeworld, which included Jasper. 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 and capable of creating spaceships, pocket dimensions, and teleporters (among others).
 * 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, 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, Communications Hub, and the Galaxy Warp among others.
 * While there has never been mention of Gems practicing any form of spiritualism, the existence of the Moon Goddess Statue along with the cloud, underwater, and Pyramid temples imply some sort of belief system.
 * While Gems are incapable of reproduction, romantic relationships do exist in their society (Such as Ruby and Sapphire, who's relationship has been confirmed to be romantic by Joe Johnston.)

Broken and Corrupted Gems
In "Ocean Gem," Pearl and Amethyst explain that "not all Gems are good" and that all of the Gem Monsters that the Crystal Gems fought up until "Mirror Gem" were in fact either corrupted or broken Gems which presumably either cracked their gems like Amethyst did in "An Indirect Kiss" or through some other means where unable to maintain humanoid form and sentience. It is possible that the corrupted Gems infesting Earth used to be followers of Rose Quartz, but eventually lost their way and became corrupted.

As of "Horror Club," the monsters that have been previously encountered are corrupted Gems, they are the following:
 * Centipeetle Mother ("Gem Glow")
 * Worm Monster ("Bubble Buddies")
 * Gem Cave Creature ("Arcade Mania")
 * Flying Monster ("Giant Woman")
 * The Geode Beetles of Heaven & Earth ("Giant Woman")
 * Giant Pufferfish (confirmed to be Watermelon Tourmaline) ("Beach Party")
 * Ice Monster ("Monster Buddies")
 * Invisible Gem ("Island Adventure")
 * Lighthouse Gem Monster ("Horror Club")

Reproduction
It has been confirmed by Rebecca Sugar that Gems don't naturally reproduce and lack reproductive organs.

In "On the Run" it is revealed that Gems from the Gem Homeworld used a canyon on Earth, referred to as "Kindergarten," to create new Gems; and that Amethyst was one such Gem. The methods used to accomplish this are as of yet unknown, but it can be deduced that it most likely involved the large bacteriophage-like machines laying Gems in the holes they drill such as the hole which Amethyst claims was "Where I came from." This process is apparently very invasive to the environment and deadly to the point where, if it was allowed to continue, it would lead to "the destruction of all life on Earth", according to Pearl in "Marble Madness". Amethyst, in a fit of anger and shame, 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. Using their shapeshifting they can perfectly replicate reproductive organs of organic beings for their "human constructs" in order to reproduce. Rose Quartz so far is the only known Gem to have done this as she did so in order to give birth to her son, Steven. This resulted in her gemstone being passed down onto her son; an action which also caused the destruction of her physical form, "killing" her.

Trivia

 * In "Jail Break", it was shown that Fusion Gems can also fuse to make other fusion gems. Garnet is a fusion gem of Ruby and Sapphire, but she can also create other fusions such as Alexandrite and Sugilite.
 * If multiple Gems stay fused for too long or have a fusion with an unstable personality, they can slowly lose their individuality. A prime example is the fusion Gem Sugilite from the episode "Coach Steven."
 * All of the known Gem weapons are medieval: Garnet has gauntlets, Pearl has a spear, Amethyst has a whip, Steven has a shield, Lion has Rose's sword, Opal has a bow and arrows, Sugilite has a flail, and Jasper has a helmet.
 * List of known Gems and their ties to birthstones (by month).
 * Garnet - January
 * Amethyst - February
 * Pearl - June
 * Alexandrite - June (Alternative)
 * Ruby - July
 * Peridot - August
 * Sapphire - September
 * Lapis - September (Alternative)
 * Opal - October
 * The gems themselves correspond with the Gems personalities.
 * Amethyst is a stone associated with love. The stone itself is associated with Dionysus, the god of wine and intoxication. Amethyst is not a clear thinker but is fun-loving.
 * Pearl is a stone associated with purity. Pearl is a mature, wise, and perfectionist person.
 * Garnet is a stone that protects from evil. Garnet is the most powerful of the Crystal Gems and often saves the day. She is also the leader of the Crystal Gems.
 * Rose Quartz is a stone associated with love and joy. Steven is the most caring, and upbeat of the gems, and Rose Quartz is mentioned to have been very loving of everything.
 * Lapis Lazuli is a stone associated with gods and power. She is a powerful Gem, nearly capable of defeating the Crystal Gems.
 * Peridot is a stone associated with the heart chakra, bringing balance and relieving stress. Peridot is shown to be level headed and calculated, if not passionate about her work.
 * Jasper is a stone associated with compassion and maternity, ironic considering Jasper's savage and aggressive temperament.
 * Their gemstone placement seems to correspond to their personalities, actions, and how they think.
 * Amethyst's gem is over her heart; she tends to be fun loving, and often does whatever she wants.
 * Pearl's gem is on her forehead; she tends to over-think things, a perfectionist mindset as well as being very intelligent.
 * Garnet's gems are on her hands; she tends to not talk often and respond through action instead.
 * Steven's gem is over his stomach; he tends to go with his gut instinct and is often hungry and like his mother he is very loving and caring.
 * Lapis Lazuli's gem is placed over the center of her spine; she sprouts wings from her gem and has been shown to be very vulnerable emotionally.
 * Peridot's gem is on her forehead; she is shown to be very intelligent (a trait she shares with Pearl who also has her Gemstone in her forehead) and dedicated to her mission.
 * Jasper's gem is placed over her nose; she is very self-centered and primal.
 * 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 gem 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. According to Mr. Gus in Say Uncle, Steven's powers are maternal, meaning his powers react to his emotion.
 * While never confirmed, Jasper may be able to summon her Crash Helmet when under a Berserker mindset, summoning it when became interested in the task at hand when Garnet made the first punch.
 * Rebecca Sugar had said that Gems have a 50/50 chance of using gender pronouns.
 * This is done regardless to what Gems identify as, as Gems don’t have gender designations amongst themselves.
 * This is demonstrated in "Ocean Gem", as Pearl called Lapis a "she".
 * Pearl also referred to Rose as "she" while reminiscing in "Rose's Scabbard".
 * In "Alone Together" Pearl comments that Steven may not be able to fuse because he's 'organic'. This would mean that Gems aren't carbon based life forms and are either most likely silicon based (as silicon is chemically similar to carbon) or a type of life form completely unknown to humans.
 * Gems physical bodies are capable of producing bodily fluids such as saliva, tears, etc. Furthermore, in "Coach Steven", Pearl can be observed to have scrapes on her "skin".
 * Their bodies are referred to by Pearl as "human construct(s)" in "Fusion Cuisine".Whatevenaregems.png
 * However it might be unlikely that Gems are inorganic, because if Gems are truly inorganic then they cannot contain biomolecules such as DNA, making it questionable that Rose could pass any to Steven.
 * Half-Gems can fuse with humans, such as Steven did with Connie to form Stevonnie, but it remains to be seen if Half-Gems can fuse with Gems.
 * You can go inside a Gem - as shown in the Comic Series Issue #5 - it is a storage place of memories and items, if you fill up a Gem with too much stuff it makes them sick.