Gems are a sentient, extraterrestrial species of inorganic creature, and one that is featured extensively throughout the My Little Universe franchise, with many of the main characters being amongst the Gem species.
All types of Gem take their form from a Gemstone, which is capable of emitting and creating a physical light projection, slightly similar to a hologram. The placement of said Gemstone varies between individuals, but the average body structure given is a bipedal, upright, Human-like anatomy. A Gems' color is influenced by the type of Gemstone it has, and while a Gem can alter its body in a matter of shapeshifting, every Gem is made with a "default" body, and it can't stay in another form without eventually changing back. Gems are capable of surviving for thousands of years, and it is unclear of their life expectancy, if they have one at all, though a Gem can be killed if their Gemstone is severely damaged beyond repair. It is revealed though that Gems are able to be saved from dying after being shattered if the gemstone is repaired and healed fast enough for the energy to remain inside, the Gem coming back as if it were just a normal reformation.
Although resembling Humans, Gems have naturally stronger physical prowess than other humanoids, and are constantly shown to be stronger, faster, and more agile than human beings. The average size for Gems vary between three to six feet tall, again much like Human beings, with the exception of the Diamonds (Yellow Diamond, Blue Diamond, and White Diamond), which can grow over ten feet tall.
While most species of Gem take the form of female and male individuals (though female is far more superior in appearance), all Gems are considered sexless and unable to sexually reproduce. The exception to this rule would be Steven Universe, Connie Maheswaran, and Blue. A Gem can be made however after a process in which a Gemstone is injected into an organic planet, and the Gemstone absorbing the energy around it for an extended period of time until it has enough to take on a physical form.
Gems are shown to live in a Caste system: in which a Gem is placed in a role depending on its Gemstone and not on an individual talent or opinion. Many Gems from Homeworld depict the Diamonds as their overlords and consider themselves inferior towards them. Many of these roles usually consist of military or aristocratic placement, though in the case of a few groups, exceptions are made to these rules if one can be found, be it either the Diamonds assigning a Gem to a different role or if there's no other Gem available for a role at a specific time.
As currently, there're two main groups of Gemkind: those on Homeworld, and a group on Earth known as the Crystal Gems, that had isolated themselves on Earth due to their refusal over the current ideals of the Diamond Authority, and follow the opposite ideologies of the caste system, as they support individualism and freedom of choice regardless of Gem type.
- Diamonds - The Diamonds are the leaders of Homeworld, and are considered by many other Gems as the highest ranking and most powerful Gem type of the entire race. Any other Gem from any other ranks takes their orders from the Diamond Authority, and any Gem to defy a Diamond is meant with punishment.
- White Diamond - The leader of the Diamond Authority. She is in charge mostly in the scientific aspects of Gem kind, establishing much of the cultural and scientific structure of Homeworld.
- Blue Diamond - The overseer of Homeworld diplomatic Gems, and the most open one towards both Homeworld and Crystal Gems.
- Yellow Diamond - confirmed to be the second-youngest Diamond, and in charge of much of the Homeworld's military.
- Pink Diamond - the youngest Diamond of the Diamond Authority, who presumed the identity of Rose Quartz during the Gem War. She founded the Crystal Gems.
- Sapphires - A type of Gem best known for their fortune-telling abilities, and their ability to see into the future. As such, they are of very high rank, and aristocratic. Sapphires aren't truly physical or intimidating however, and are often guarded by larger Gems.
- Zircons - Homeworld's more diplomatic Gem, Zircons are often placed in roles of lawyers, and often have a more open and wide mind than other Gems.
- Rubies - A type of low-ranking "Foot Soldier" Gem. Bands of these Gems are often used in fighting alongside traditional Quartzes.
- Peridots - Peridots fill in the similar role to Fulgurites as the technicians of Homeworld, and became the primary Gem for the role sometime after the Gem War. As evident with Peridot, Peridots made in Era 2 are given technological enhancements and were considered powerless when compared to their Era 1 counterparts. It is also revealed by Yellow Diamond that Peridots have a natural trait of being together.
- Fulgurites - Fulgurites were the previous main technicians during Era 1 of Homeworld, prior to Peridot creation. According to The Deep Six, both Fulgurites and Peridots did work together on the same projects at a point.
- Jades - Jades are Homeworld's reporters, mostly known for providing information through literary works and keeping track of events through words.
- Emeralds - Emeralds on Homeworld are considered high-ranking captains, and often pilots for many of Homeworld's spaceships.
- Quartzes - Quartz Gems are the soldiers of Gem kind, and are considered the most common Gem type on Homeworld due tp the numerous sub-types to be featured.
- Agates - A type of Quartz described as to be "terrifying" by White Diamond.
- Amethysts - Amethyst are described as a "barbarian group" of Gems, to be released and basically run amok in the battlefield without much order.
- Carnelians - A type of Quartz mentioned by White Diamond.
- Citrines - A type of Quartz first mentioned by White Diamond. Revealed in The Games of Era 3, Citrines are made as gunners, having a natural talent for marksmanship.
- Jaspers - A type of high-ranking Quartz Gem.
- Rose Quartzes - A type of Quartz apart of the "Healing group" of Gems, and were once in charge of the Human Zoo prior to the Gem War. They're more defensive than offensive.
- Star Quartzes - A type of Quartz Gem. It is unknown what role it has on Homeworld.
- Pearls - Pearls are considered the lowest-ranking Gem on Homeworld, and are typically made as servants to other high-ranking Gems. Typically a Pearl barely has any power, if any at all, though the exception to this rule are those Pearls under The Diamond Authority, who're seen ordering quartz soldiers.
- Flints - Flints are a previous type of Gem of presumably higher ranking as guardian Gems. White Diamond hinted that Flints are a very rare Gem type, with Flint being the only Gem with true Flint components within him.
- Gem Hybrids - A type of Gem made of two different Gems upon creation. These are not to be confused with Gem fusions. Most Gem Hybrids are under White Diamond's court and reside in the White Diamond Space Station.
- Cluster Gems - A type of Gem resulted from force fusion experiments, often appearing as abominations.
- Corrupted Gems - A Gem who is suffering from Corruption, and lost its sentience, and as such becoming more feral.
- Harvested Gems - A Gem who's been sentenced to being harvested. These Gems are sentient, but are made in such a way that they resemble Gem Objects.