Gemstones

"Gemstones" are the most vital part of any Gem. They appear as gems in various cuts and shapes located on any part of a Gem's physical body (or "human construct").

Description
The Gemstones are, in essence, the Gem creature/being itself. Their physical bodies are merely a projection from within the Gemstone, much like their weapons and outfits. As a result any damage to their physical bodies is merely an inconvenience to the Gem as they have to spend time regenerating/recuperating before they can manifest it again. On the contrary, any slight damage such as a crack to the Gemstone results in a serious, and often crippling, injury to the Gem. It can interfere with their magical Gem powers, as Lapis was unable to summon her water wings with her Gemstone 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 got more and more cracked in "An Indirect Kiss". The results of a Gemstone being completely destroyed is currently unknown.

Abilities
Gems can manifest things from within their Gemstone; the most important being their personal weapons and their physical bodies. Pearl and Peridot have the ability to store and withdraw objects (such as a roll of police tape or an EMP device) in their Gemstone, but it is currently unknown if that ability is unique to them or if it is shared by all of Gemkind.

Gem bubbles have a stasis-like effect on Gemstones; when "bubbled" by another Gem, the Gemstone is prevented from regenerating/manifesting it's physical body or weapon, essentially being imprisoned indefinitely until the bubble breaks.

Gemstones also find a use in "Gemtech"; 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", and a Gemstone also powered the mechanical apparatus in the Pyramid Temple in "Serious Steven". It should be noted that the ethical implications of using Gemstones in this manner has yet to been fully addressed in the series; however Lapis' case was forced servitude as she desired escape as well as referred to her existence within the mirror as "imprisonment". The experience also severely traumatized her to such a degree that it left a deep psychological scar that affected her personality.

Culture
As one would expect, the Gemstone of each individual 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 prior to the events of the episode and, due to Steven having inherited his mother's Gemstone, she instantly thought he was his mother shape-shifted into a weak, human boy which confused and infuriated her.