Gemstones

Gemstones are the core components of any Gem. They appear as literal gemstones in various cuts, shapes, and colors located randomly on any Gem's physical form.

Description
The gemstones are, in essence, the Gem being itself. According to Pearl in "What Are Gems?", their physical bodies are merely a hologram with mass from within the gemstone, much like their weapons and outfits. Garnet states in "Steven the Sword Fighter" that if the physical body (which is just an illusion) of a Gem is severely damaged or injured, it retreats to its gemstone to regenerate and project a new body form. All Crystal Gems besides Steven have been shown to regenerate.

In contrast, any slight damage to the gemstone, such as a crack, results in a serious and often crippling injury to the Gem. It can interfere with their magical Gem powers, as Lapis Lazuli is unable to summon her water wings while her gemstone is cracked in "Ocean Gem". It also interferes with their ability to manifest/control their physical bodies as Amethyst lost more and more control of hers as her gemstone is continuously cracked in "An Indirect Kiss". Destroying a Gemstone effectively kills the Gem (although it retains some magical properties, such as the Gem Shards in "Frybo" and "Secret Team", the Smoke Monster in "Together Breakfast" and all the gem shards they've encountered).

During Gem Fusion, all participants' gemstones shift colors to match each other. If the participants of the fusion are the same Gem type, the resulting fusion is just a larger version of the Gem.

Multiple Gems with the same gemstone may exist. Gemstone placement appears to vary from Gem to Gem, even if they are of the same gemstone. All Gems of the same gemstone will have the same cut to their gemstone; the Diamonds and Pearls are exceptions to this. Gems of the same gemstone may even have different summoned weapons.

Abilities
Gems can manifest things from within their gemstone, with the most important being their personal weapons and their physical bodies. Pearl, Garnet and Peridot have the ability to store and withdraw objects (such as a roll of tape, temple key or an EMP device respectively) in their gemstone, but it is currently unknown if that ability is unique to them or if all Gems share it.

Gem bubbles have a stasis-like effect on gemstones; when "bubbled" by another Gem, the gemstone is prevented from regenerating/manifesting its physical body or weapon, essentially being imprisoned indefinitely until the bubble bursts.

Gemstones also find use in Gem technology. They are used as power sources for various objects such as Lapis' gemstone being used to power the magical mirror in "Mirror Gem". A corrupted gemstone also powered the mechanical apparatus in the Pyramid Temple in "Serious Steven".

Culture
As one would expect, the gemstone of each Gem is a core aspect of Gem culture. The Gems are not only named after their gemstone but are also recognized by other Gems by it. In "The Return", Jasper showed that she had known of Rose Quartz before the events of the episode and, due to Steven having inherited his mother's gemstone, she instantly thinks he is his mother shape-shifted into a weak, human boy which confuses and infuriates her. Individuality is a rare concept among Gems, as there is evidently little to differentiate Gems (aside from gemstone type) other than a serial number based on facet and cut.

It also seems to be customary for a Gem to keep their gemstones exposed, as all full uncorrupted Gems seen so far in the series have had theirs at least partially visible, to the point of altering the Homeworld uniform.

Trivia

 * Diamonds are the only known Gems of the same type with different shaped gemstones.
 * List of known Gems and their ties to birthstones (by month).
 * Garnet - January
 * Steven/Rose Quartz - January (Alternative)
 * Amethyst - February
 * Yellow Diamond/Blue Diamond/Pink Diamond/White Diamond - April
 * Pearl/Blue Pearl/Yellow Pearl - June
 * Alexandrite - June (Alternative)
 * Ruby - July
 * Peridot - August
 * Sardonyx - August (Alternative)
 * 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 was very loving and had a joyful personality.
 * 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.


 * Although the gemstone being exposed is largely cultural, given that some corrupted Gems have had them internally, Steven once expressed discomfort as a baby when his baby onsie covered his Gemstone.


 * Their gemstone placement seems to correspond to their personalities, actions, and how they think.
 * Amethyst's gem is near to the location of a human heart; she tends to be fun-loving and often does whatever she wants.
 * Bismuth's gem placement is quite similar, in the sense that she "follows her heart".
 * Pearl's gem is on her forehead; she tends to over-think things, has a perfectionist mindset, as well as being very intelligent.
 * Garnet's gems are in her hands; she tends not to 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.
 * Yellow and Blue Diamond have their gems on their chests; as they are considered "matriarchs" and have a high placement in the caste.