Gem

"Gems" are an alien race of "magical" beings that play a central role in Steven Universe.

General Description
They are sentient gemstones that can project a tangible, typically human-like form. They are an intergalactic race which 5,750 years ago maintained several outposts on Earth, with plans to completely colonize the planet, but were driven off by Rose Quartz's rebellion, leaving the Crystal Gems and the corrupted Gems as the only Gems on the planet, except for a small group of stranded Gems from the Gem Homeworld who for the most part arrived later.

Though pure Gems are referred to in feminine terms and commonly have feminine traits, Gems are a genderless race, with Steven Universe being the first male Gem to exist, as well as the first human-gem hybrid. Despite this, Gems with more masculine appearances and even voices are not completely unheard of.

Appearance and Gender
Crystal Gems generally take on a feminine or androgynous human-like form, notably distinguished by the lack of gender-defining traits such as breasts unless they were added by choice. For the most part, they appear to lack external ears, and many Gems may lack a nose or have only one eye. The forms they take are only constructs their gem creates for them, which follows restrictions set by their biological caste. The Gems appearance varies from Gem to Gem but their colors are mainly composed of the color palette of the gem they posses (e.g. Garnet is mainly red, Amethyst is mainly purple/violet). The Gems have a permanent form that they keep all the time, but if that form is destroyed or has taken too much damage, they retreat into their gem and create a new one. Their appearance may change upon regeneration if the Gems wanted to "reinvent" themselves, but few Gems are capable of reforming far outside the restrictions of their original body.

Gems are not biologically male or female, or have female and male designations among themselves. As a rule they use feminine pronouns for linguistic purposes, with Steven being the only male and possibly the only Gem with a gender identity at all due to his human half, as well as the first gem hybrid. It should be noted that when Amethyst is in her "Purple Puma" form she uses male pronouns, but this is likely a similar situation to stage names with differing pronouns from the person behind the name (and to date, there hasn't been a pure gem with a male appearance or personality). Fusions between Steven and anyone who uses she/her, human or gem, apparently uses they/them.

The Gem's usage of gendered pronouns with one another does not deter the fact that they are all just Gems first and foremost, and was stated by Rebecca Sugar to be similar to the countless "all-male" races in fiction which all use he/him despite having no basis for gender within their species. Notably, Gems unfamiliar with the concept of gender have been shown to refer to the rare Gems who do not use she/her, such as Steven, by feminine pronouns--from the Gem perspective, feminine pronouns are essentially neutral pronouns that everyone uses.

History
All Gems have superhuman powers such as shape-shifting (with the exception of era 2 gems), Gem bubbling, weapon summoning or elemental control, and Gem fusion. For thousands of years, the Crystal Gems have used these abilities to defend the planet Earth from countless magical threats. One of the Crystal Gems (and former leader), Rose Quartz, gave up her physical form to give birth to a half-human child, Steven Quartz Universe. Garnet, Amethyst, and Pearl consider Steven an important member of the Crystal Gems, and the three have taken it upon themselves to raise and teach him how to use his powers.

In several episodes, Pearl references that there are/were many more of their kind, but never elaborated on the absence of other Gems on Earth, implying that they all may have died or disappeared. In the episode "Ocean Gem," it is revealed that there are in fact other Gems, and that the monsters that the Crystal Gems fight to defeat are former Gems that had gone corrupt. As of now, 6 uncorrupted non-hybrid Gems remain on Earth (Counting Garnet as two gems, and Peridot and Lapis).

As revealed in "Space Race", there are more Gems on different Gem-controlled planets. The Galaxy Warp was the main hub that was used to travel off of Earth to different Gem planets, but currently all the warp pads are broken. This reveals why only the Crystal Gems reside on Earth.

Culture

 * Pearl points out in "Tiger Millionaire" that, as Crystal Gems, they are not allowed to use their powers on humans. Although, that was broken when a human named Ronaldo kidnapped Steven.
 * Whereas the Crystal Gems incorporate stars into their clothing, Homeworld Gems use diamonds.
 * The typical way for a Homeworld Gem to address a Diamond is "My Diamond" while either bowing or saluting.
 * Sapphires are addressed as "Your Clarity" or "Your Grand Clarity" by lower castes.

Biology
Gems seem to be mineralistic silicon-based lifeforms due to primarily being living gemstones. A gem's signature gemstone is positioned somewhere on their physical forms, such as the forehead, palm of the hands, chest, back or navel (depending on the individual). The gems are capable of shape shifting their entire bodies, or at least their appendages, into any shape; however, this is known to consume a lot of energy and leave a Gem exhausted when done for too long. They are functionally immortal, similar to vampires, as Pearl stated they do not age, meaning they won't die from old age, but can die by other means, such as being shattered. If a gem is severely injured, their body dissipates in a burst of dust or smoke, leaving behind their true body--the gemstone--which is vulnerable and unable to move until the gem finishes regenerating her body (unless their encased in a gem bubble, which can disable regeneration). The time-span of this recovery status can vary depending on the gem's personality and sense of patience, as while Pearl took two weeks to heal due to being cautious, Amethyst preferred to reform in mere seconds; the process can also be rushed, but this would cause a Gem to regenerate with deformities. Their signature gemstones also seem to be weak spots as if they were damaged the owner's forms would get messed up, as is the case of Amethyst's gem getting cracked caused her form to morph itself in a crazed state. Gems also never suffer from hunger or sleep and as such have no need to perform these daily duties, but are nonetheless capable of doing these tasks.

Gems are also capable of Fusing into each other in order to become a gigantic version that can comprise of two or more gems in number. The fusion forms often have more than one pair of arms (or legs in Malachite's case), depending on the number of gems the fusion is made of and the compatibility of the individuals, though this only seems to apply to separate types of gems, as when two or more rubies fuse they only look like a larger version of a normal ruby, meaning that fusions made up of the same caste resemble larger versions of themselves. Most of the time gems Fuse during a crisis. Some of the fusion forms though seem to be unstable' as in the case of Sugilite, the fusion of Garnet and Amethyst, who is incredibly aggressive that neither Garnet or Amethyst can get possession of themselves in the form and presents a danger to everyone around her.

New gems were created from facilities called Kindergartens. While biological reproduction is an alien concept to Gems, it is not impossible for them; while Gems can't reproduce with each other, at least one was able to create Gem-hybrid offspring--although it should be important to note that this Gem was a Diamond, a type of Gem known to have life-related powers not seen in other Gems. Through shape-shifting, they can perfectly replicate reproductive organs of organic beings for their "human constructs" in order to reproduce. Pink Diamond, known at the time by her alias 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". Similarly, they can also experience romantic feelings at least, as seen with Ruby and Sapphire.

Gems may have been created by another species, as they are commonly stated to have been designed; however, this could also be a sign of them being genetically engineered from a past form. They're unaffected by changes in gravity, unlike humans, and according to Peridot they can adapt to any planetary-gravity without any drawbacks. They do not need to breathe, but do appear to have lungs for speaking purposes, and are not immune to gasping for breath.

While Gems are sentient, they can be become feral and animalistic: these feral-gems are known as "corrupted", as stated by Pearl. Many corrupted-gems tend to adopt appearances and personalities of wild animals. Nephrite for instance was formally a normal gem with a humanoid-body, but when she became corrupted she morphed into a centipede-like beast, both physically and mentally. The gem-corruption also seems to function like a disease, as when Jasper fused with a feral-gem she had captured to battle Smokey Quartz, she showed evidence of getting infected with the corruption after defusing and eventually morphed into a monster herself. Corruption is not known to occur naturally, and the origins of all known Corrupted Gems can be traced back to an attack on Earth which was intended to kill every Gem on the planet but failed.

Fusions
It is revealed in "Giant Woman," that the Gems are able to fuse together into even more powerful Crystal Gems. Here are the ones shown so far:
 * Ruby + Sapphire = Garnet
 * Amethyst + Pearl = Opal
 * Garnet + Amethyst = Sugilite
 * Garnet + Pearl = Sardonyx
 * Steven + Connie = Stevonnie
 * Steven + Amethyst = Smoky Quartz
 * Steven + Pearl = Rainbow Quartz 2.0
 * Steven + Garnet = Sunstone
 * Rose Quartz + Pearl = Rainbow Quartz
 * Pearl + Ruby = Rhodonite
 * 6 unknown gems = Fluorite
 * Jasper + Lapis Lazuli = Malachite
 * Jasper + Ocean Jasper/Snow Monster = Zebra Jasper
 * Left Topaz + Right Topaz = Topaz
 * Garnet + Amethyst + Pearl = Alexandrite
 * Garnet + Amethyst + Pearl + Rose Quartz or Steven = Obsidian.

Gems cannot fuse with humans, as shown in "We Need to Talk". However, Gem-human-hybrids can fuse with humans, as Steven did with Connie to form Stevonnie. Hybrids can fuse with pure Gems too, as Steven formed Smokey Quartz with Amethyst, Rainbow Quartz 2.0 with Pearl and Sunstone with Garnet.

Even feral, corrupted gems are capable of fusion, as Jasper fused with the Snow Monster to form Zebra Jasper.