Violet Diamond is a defective Homeworld Gem, and an original Gem created by GemCrust.
Violet Diamond has a violet complexion. She has an overall thin build, with the exception of her spherical upper and lower torsos. She possesses neon pink skin and dark purple, short hair, that has a big flick in the back. She has wide purple eyes with lilac pupils, violet eyeshadows above them, and a slightly pointy nose. She has large purple shoulder pads and white arm-length fluffs. She has small plump lips and an elongated jaw. Her gemstone is embedded in her sternum.
As for her outfit, Violet Diamond wears a pink and violet bodysuit, with large purple shoulder pads and white arm-length fluffs. Her pants are divided into two colors and end in pink "socks."
Nothing is known about Violet Diamond's personality yet.
Before the creation of Red Diamond, Violet Diamond emerged a defective Gem: she lacked the powers a Diamond needed to have. For this reason, the moment she formed she was subdued, poofed and bubbled by Yellow Diamond. While this situation was witnessed by a few high-class Gems around, Violet's name was buried away so that only Yellow herself and White Diamond knew she had ever existed.
Upon being bubbled away, Violet Diamond was converted into a Gem Key to power various Gem-tech and items, allowing for her to be used in a multitude of ways. Her gemstone was then locked away in one of Yellow's chambers.
During her shenanigans on Homeworld, Violet Diamond's gem was managed to be taken hold by Ice. She fused with it, as Violet wouldn't reform, and together they formed a new being. Although the fusion didn't last long, Violet Diamond came out of her gem safe and sound.
It is unknown whether Violet Diamond possesses standard Gem abilities, aside from fusing. She's said not to have any abilities, and thus be weaker than other Diamonds, the reason why she's considered defective.
She's more or less powerful when compared to other Gems, but not as powerful as a real Diamond.
Ice first came to know of Violet Diamond's existence when she overheard a few Gems discussing her position, during her adventures with the Off Colors in the abandoned Kindergarten. According to them, an off-color Diamond was being held in one of Yellow Diamond's chambers, thus, after taking it to the Rutile Twins, they decided to try and rescue her. They were unsuccessful, though, because only a Diamond could enter the chamber where Violet Diamond was being held.
Somehow, Ice got hold of her gemstone. Since she wouldn't reform, similar to what Steven Universe did during the events of "Change Your Mind, Ice fused with her gem, forcefully pulling her out. Naturally, they fused, but their fusion didn't last long.
It has been stated that Violet Diamond will become a Crystal Gem once Ice sends her back to Earth.
GemCrust says he has plans to rework "Violet Diamond's entire being", due to her being made before Pink Diamond's reveal, and thus not fitting into his canon, seeing as Pink looked different from the others and was nonetheless loved and accepted.
As of February 6th, GemCrust has revamped her.
The fuss over violet and purple diamonds is recent as far as controversies go. Collectors of fancy color diamonds could only dream of owning these colors until the discovery of violet diamonds in Australia in the 1980s and a fluke find of purples in Russia a decade later. Yet even then, scientists doubted their eyes.
Collecting and Classifying Fancy Coloured Diamonds refuses to recognize the violet diamond as a separate and distinct category. But it’s not because such stones are too purple. It’s because they’re too blue.
Author Stephen Hofer says that at the time of the book’s publication in 1998 he had not yet found any diamonds that measured in the violet region of the spectrum using an electronic colorimeter. To him, most violet stones measured in the blue and were best classified as such.