Gems

Not to be confused with the Crystal Gems, a group of Gems, or gemstones. "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 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 the Crystal Gems.

Singular

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

Hybrid

 * Steven

Fusions

 * Garnet
 * Opal
 * Sugilite
 * Alexandrite
 * Malachite
 * Rainbow Quartz

Hybrid Fusions

 * Stevonnie

Forced Fusion

 * Cluster

Corrupted Gems

 * Centipeetle Mother
 * Gem shards
 * Worm Monster
 * Gem Cave Creature
 * Big Bird
 * Heaven Beetle
 * Earth Beetle
 * Giant Pufferfish (Watermelon Tourmaline )
 * Ice Monster
 * Invisible Gem Monster
 * Lighthouse Gem Monster
 * Tardigrade Gem Monster
 * The Slinker
 * Crab Gem Monster

Unknown

 * Yellow Diamond
 * Sardonyx

Description
Gems are characterized by their gemstone, which is embedded somewhere on their body. Each Gem shown thus far is unique (excluding Pearl's/Peridot's gem placement), and the gemstone seems to be analogous to the brain or CPU. Gems generally take the form of feminine humanoids, with their palettes mirroring the color palettes of their gemstone.

Gems have the ability to customize their physical forms (which appear to be some sort of hard-light construct) at will, with their only constant feature being their gemstone and colour palette. Because of this, all Gems are inherently sexless. 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 physical forms mimic all attributes to the human body, including major vital organ systems. They, however, do not need to eat/sleep to survive.

Gems have numerous abilities, such as weapon-summoning, fusion, the power to 'store' material in their gemstones (it if this ability has a limit), and the ability to conjure bubbles. All Gems seem to have the ability to harness/transfer 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 a bursts of energy through her whip(s). In addition, many Gems have specialized abilities as well, such as Lapis Lazuli's ability to manipulate water, and Pearl's ability to manipulate sand.

Gems are functionally immortal, unable to die from aging or food-poisoning. Although, Gems can still be "killed" if their gemstone is destroyed. When a Gems' physical body is badly injured, they will retreat into their gemstone to regenerate. The regeneration time depends on the individual Gem. Pearl's regeneration lasted two weeks, but Amethyst's have taken mere seconds, although she did suffer physical deformities as a result. It seems that when a gemstone is bubbled, it prevents regeneration from taking place. Furthermore, Gems are superhumanly strong and durable. For example, in "House Guest", Garnet effortlessly lifts up Greg's van, and in "Keep Beach City Weird", Ronaldo hurts his hand when Pearl blocks his punch with her open palm.

If their gemstone is damaged, a Gem may go through glitch-like deformities. It is also noteworthy that a Gems' gemstones can be used as a power source, even if damaged. Gem Shards function similarly, 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. Gem Shards that have also been fused together overtime of compression will also regenerate and glitch into The Cluster.

Culture

 * There are two known groups of Gems: Homeworld Gems and Crystal Gems.
 * The 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", whose agents include Peridot, Jasper, Lapis Lazuli, and their currently unseen superior known as Yellow Diamond.
 * 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, 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 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 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 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 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.

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 Injectors laying Gems in the holes they drill, such as the hole which Amethyst claims, "This is where I was made." This process is apparently very invasive to the environment and deadly 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, so far, is the only 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.

Corrupted Gems
In "Ocean Gem," Pearl states, "All Gems aren't necessarily good". Gem Monsters are in fact either "corrupted"/"broken" Gems which, presumably, were unable to maintain humanoid form and sentience.

Trivia

 * In "Jail Break", it was shown that fusions are capable of fusing. Garnet is a fusion, but can still create fusions with others.
 * If multiple Gems stay fused for long periods of time, or have a fusion with an unstable personality, they can slowly lose their individuality.
 * All known Gem weapons are medieval: Garnet's gauntlets, Pearl's spear, Amethyst's whip, Steven's shield, Rose's sword, Opal's longbow, Sugilite's flail, and Jasper's crash-helmet.
 * Some Gems are connected to birthstones (by month).
 * Garnet - January
 * Amethyst - February
 * Jasper - March (alternative)
 * Pearl - June
 * Alexandrite - June (alternative)
 * Ruby - July
 * Peridot - August
 * Sardonyx - August
 * Sapphire - September
 * Lapis Lazuli - 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 mature, wise, and perfectionistic.
 * 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, in the midst of a cracked gem.
 * 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.
 * However, the gemstone is also associated with fire, so this could lead to Jasper's ill-temper.
 * 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), 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 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. According to Mr. Gus, Steven's powers are maternal, meaning his powers react to his emotion.
 * Jasper may be able to summon her weapon when under a berserk mindset.
 * Ian Jones-Quartey has stated that Steven is the first Gem to use masculine pronouns.
 * Gems don’t have gender designations among themselves, instead using feminine pronouns.
 * 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".
 * Gem's 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".
 * Each individual Gem seems to have a blood color that matches their own color palette, with Pearl's blood being a light-blue, and Amethyst's blood being a dark-purple. This is observed based on the color of a Gem's blush.
 * Pearl referred to their bodies as "human construct(s)" in "Fusion Cuisine".
 * If Gems are truly inorganic, then they cannot contain biomolecules such as DNA, making it questionable that Rose could pass any to Steven.
 * 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".