The "Crystal Gems" are a group of Gems who, unlike the rest of their kind, seeks to protect the Earth instead of invading it and are the self-proclaimed guardians of humanity. The title, Crystal Gem, is what distinguishes them from the homeworld Gems.
- Garnet: The de facto leader of the group and a fusion Gem who wields a pair of gauntlets.
- Amethyst: The care-free member of the group who wields a three-tailed whip and the youngest aside from Steven. Unlike the other Gems (besides Steven, who is also from Earth) Amethyst was made on Earth.
- Pearl: The intellectual member of the group who wields a spear.
- Steven Universe: A half-human member of the group who can summon a shield and a bubble, also the youngest. Son of Rose Quartz, the founder of the Crystal Gems, who gave up her physical form to give birth to him.
Known Crystal Gem Fusions
- Opal (Revealed in "Giant Woman"): A tall and slender Gem who wields a bow. Fusion of Pearl and Amethyst.
- Sugilite (Revealed in "Coach Steven"): A gigantic and bulky Gem who wields a flail. Fusion of Garnet and Amethyst.
- Alexandrite (Revealed in "Fusion Cuisine"): A tall six-armed fusion of Garnet, Pearl, and Amethyst.
- Stevonnie (Revealed in "Alone Together"): A teenage-looking fusion between Steven and Connie, a human.
- Garnet herself is a fusion of Ruby and Sapphire, as confirmed in "Jail Break".
HistoryThe exact origins of the Crystal Gems are unknown. What is known is that for about 6,000 years, the Crystal Gems have used their abilities to defend Earth from countless magical threats. However, Rose Quartz, leader of the Gems, and a great admirer of humanity gave up her physical form to give birth to a half-human child, Steven Quartz Universe. The other Crystal Gems, 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, only six uncorrupted Gems remain on Earth, counting the two Gems fused into Garnet and Lapis Lazuli.
The episode "Space Race" revealed that there are more Gems, but on different Gem-controlled planets. The Galaxy Warp was the main hub that was used to travel off-planet to other planets. Currently, all of the warp pads in the Galaxy Warp are broken.
It is implied that the Crystal Gems may be exiles or outlaws from the rest of Gem society. In "Space Race", Pearl makes it clear the Crystal Gems are trapped on earth. In "Warp Tour" however, the appearance of Peridot and fixing of the warp pads greatly upset the other Gems who began to panic because "they're coming back".
"On the Run" revealed that Gems had previously built machines which were capable of 'manufacturing' new gems in specific places called "Kindergarten". Also, it was said that the Homeworld wanted to do something with the Earth, but the Crystal Gems rebelled, halting their plans. Because of this rebellion, the Crystal Gems chose to stay on Earth to protect it from any possible threat, even if it meant they could never return to their previous 'home', and to prevent gems from the Homeworld from returning to Earth.
- List of known Crystal Gems and their ties to birthstones (by month).
- "Rose's Scabbard" revealed that Rose Quartz had founded the Crystal Gems to oppose the Homeworld's invasion of Earth. At the time, the Crystal Gems had many more members, enough to compose an army.
- In "The Return", it's heavily implied that the Crystal Gems were larger in number as revealed by both Greg and Jasper, in which Rose Quartz could only save a handful of her closest friends during the devastating battle to protect Earth.
- In "On the Run", it is revealed that Rose Quartz, Pearl, and Garnet originally came from the Gem Homeworld, whilst Amethyst was formed on earth in a Gem Kindergarten.
- Amethyst is the only good gem known to have been "made" in the Gem Kindergarten, though there were hundreds of parasitic ones.
- Rose seems to have been an outlier in the gem world, her compassion for other life forms does not seem to be shared by her fellow gems and her love of humanity was seen as unorthodox.
- During Rose's original rebellion there were many more Crystal Gems on Earth than there are now, after the Homeworld were defeated and driven off Earth it's unclear what became of the Gems who elected to stay on Earth (most likely, they became corrupt).
- The name "Crystal Gems" was probably adopted after the war as Peridot seemed unfamiliar with the name in "Marble Madness".
- 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 "dance" of a flower petal 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. In "Gem Glow", the joy associated with eating Cookie Cat ice cream was what summoned it. In both Ocean Gem and The Return appearances, he summoned it when it was needed to protect those he loved from a large threat, much like his bubble in "Bubble Buddies".
- Steven is the only member of the Crystal Gems whose skin isn't the same color as his gem, though his skin still exhibits a pink and reddish hue.
- 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 and be a perfectionist.
- 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.
- All Crystal Gems except for Ruby and Sapphire have stars located somewhere on their outfits. It's interesting to note that in the flashback in "Story for Steven" from before Rose died, none of them had stars except for Rose herself.
- Steven: on his t-shirt.
- Garnet: on the chest area of her body suit.
- Amethyst: star-shaped holes on her leggings.
- Pearl: on her shirt.
- Opal: on the draping section of her shirt.
- Rose Quartz: star-shaped hole on the stomach area of her dress.
- Sugilite: ragged, star-shaped holes on her leggings and painted on her nails.
- Alexandrite: special four-pointed star-shaped cutouts on her leggings and star-shaped hair.
- Steven may never develop the ability to shapeshift in the same way the Gems do because his body is physical, whereas a Gem's body is more of a "projection" on the physical plane.
- According to Rebecca Sugar, Gems do not need to eat or sleep, but they can enjoy doing so anyway.
- The gemstones themselves seem to correspond with the Crystal Gems personalities.
- Rebecca Sugar and Ian confirmed that all gems are sexless (with the exception of Steven) and use female pronouns to refer to one another.
- 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".
- The 50/50 rumor was a misunderstanding, meaning, there was a 50/50 chance she had picked male pronouns for all gems, or female pronouns for all gems, and in the end, she picked female.
- It is also stated many times that Gems can take on any form they want, meaning they can appear masculine but will still use female pronouns.
- Rebecca Sugar also confirmed that the crystal gems are somewhat like her, especially Pearl.
- Rebecca Sugar confirmed that each of the Crystal Gems is based off of one of the stages of the human emotional development spectrum. 
- Steven is codependent.
- Common in most children as children are dependent on their parents or any adult figures on practically anything and everything, as they are expected to be.
- Amethyst is counter dependent; the explorer and rebel, fighting authority even if it's a bad idea.
- Common in teens and young adults. People here know that they have free will and will tend to distrust and challenge authority. Known as the rebellious stage.
- Pearl is group-dependent; the responsible manager, legalistic to a fault.
- Group-dependent people are ready on taking on responsibilities and expects others to be group-dependent as well. Tends to be obsessed with the notions of obligation and duty.
- Garnet is independent; free< to take on the burdens of others, can be a bit reckless, and is understanding of the growth that risk-taking can give as well as its limitations.
- Tend to be merciful, and kind, and generous. They will help people because they want to, and they will not help people because they do not want to.
- One can also argue that Rose Quartz is transcendent; kind and loving to a fault. Uses everything in her power to help those in need.
- Master of Empathy. Understanding in all situations and acts accordingly to the given situation. Merely acts to the best of their ability, understanding the limitations of their own understanding. But in being emotionally mature their actions tend to flow out in proper response to most any situation. Sympathetic when they should be. Angry when they should be. Forgiving when they should be.
- Steven is codependent.
- All the gem's fighting styles are based off of different dances: Pearl (Ballet), Garnet (Waacking), and Amethyst (Dancehall and Club Dancing). This might also have something to do with how they synchronize before fusing.
- The rule that the Crystal Gems can't use their powers on humans was broken in "Keep Beach City Weird" when they attacked Ronaldo, but in that case an exception was probably made since they were trying to save Steven.
- In "Winter Forecast", it is revealed that Garnet can pass her future vision onto other Crystal Gems temporarily by giving them a kiss to the forehead.
- It is currently unknown whether or not if this ability is exclusive to Garnet herself, or is shared throughout the gem race and if you can pass it on in different ways.
- Each gem also has their own instrument associated with them. 
- In "Story for Steven", before Steven was born, the Crystal Gems were particularly antisocial to the humans of Beach City, keeping a fence up to keep humans out of that section of the beach.
- Rose Quartz would be a considerable exception to this, as she visited other parts of the beach and saw Greg's concert, but became nervous when he insisted on following her.
- Pearl was confused and mildly bewildered by his presence, simply referring to him as "human" or "it"
- Amethyst acts similar to a child, asking him various questions and messing with him in different ways.
- Garnet intended on evicting him from the temple as soon as she saw him, treating him as an intruder (which he technically was), threatening him with violence but was put to a halt when Rose Quartz appeared.