While not much is known about Garnet's specific origins it is known that, thanks to her being a gem, that she's well over a century old. It has also been revealed that she is the fusion of the gem lovers, Ruby and Sapphire.
Garnet is often shown to be very cool and collected in most situations. Like most of the gems she can be somewhat ignorant to human culture, but she doesn't mind it. She has also shown to sometime break her cool in desperate situations.
Garnet first appears as a cartoon character on Cartoon Network's "Steven Universe". She was created by Rebecca Sugar, former writer for another Cartoon Network series: Adventure Time. The show premiered in 2013.
Garnet made his first comic appearance in Adventure Time 2013 Spoooktacular #1, and he would later be a main character in the comic series's titled, "Steven Universe".
Garnet is the result of a fusion between Ruby and Sapphire. She has all of their powers and abilities.
Garnet, being a gem, is able to shape shift, has super strength, high resistance to heath, and has she process her own gem weapon which are, in her case, a set of red large gauntlet. She can also fuse with other gems to take a stronger form. And if she ever gets severally harmed, she can retreat into her gems in order to regenerate. But if that happens, Ruby and Sapphire will be separated, and most fuse again in order to become Garnet once again.
Garnet's body is in reality a projection from her gem stones. If her stones get's cracked, it will actually hurt her, and can even kill her.
Garnet also has the unique power known as "Future Vision." It allows her to see multiple possible future outcomes, even if they are unlikely. Her future vision seems to operate at will and with only specific details that she is looking for.