Aquamarine is another gem from the gem homeworld, and is as old as Rose Quartz and some of the other Crystal Gems. It isn't known if she had fought or not in the war, but it is true that she had been there during a couple of the battles that had taken place, mostly as an attempt to protect her friends. Though, it is known that Aquamarine is a bit of a friendly gem, and is a peaceful one too. However, while Aquamarine shared views with Rose Quartz, she had never become a Crystal Gem and had remained loyal to her planet; mostly only staying for Emerald. Aquamarine fights with a metal claw, her gem being located on the back of her hand and heart-cut.

Aquamarine generally is very relaxed, laid back and peaceful. There is seemingly nothing that bothers her, but that is exactly what she bottles up inside. Even from the beginning, she was always a peaceful gem, and had always wanted harmony. Usually in her spare time she enjoys being alone, and isn't known to have feelings outside of happy and content. With this, she cannot connect with other gems that may seem more emotional, one of those being Emerald; who is usually at constant need of someone. However, despite this, Aquamarine is very possessive and obsessive, dubbing things as "hers". She is considered almost completely fearless, but also almost crazy due to her possessiveness. She does whatever it takes to keep someone she cares about near her; and doesn't like being considered second best.

She is always found clinging to Emerald's side, and almost refuses to leave her. Aquamarine isn't a friend of Topaz, and is, as a matter of fact, very jealous of him due to Emerald's feelings for him. However, Aquamarine usually tries to live through times where she must speak or be around Topaz. Though, she never acknowledges his existence anymore, and almost ignores him, barely even taking notice that he had walked into a room. Aquamarine knows who Jasper and Peridot are, however, it isn't known if she has met them personally. However, Emerald has stated before that they had both met Peridot before; with Jasper only meeting Emerald during the war.

After crash landing on Earth with Topaz and Emerald, Aquamarine was distraught when she realized that she was completely isolated and faraway from Emerald. Her only plan was to try and find Emerald and get off the planet; planning on lying and saying that Topaz had become lost, and that she had thought he had perished. Though, she wasn't lucky and hadn't found Emerald like she planned, only stumbling upon the abandoned kindergarten after a week.

*Emerald likes to call Aquamarine "Aqua" or "Mariny"