Aquamarine

Here's Aquamarine.
Although she is a relative of Diamond burst, Aquamarine is a very regal pony, and is thought of highly by the other crystal ponies. Although Aqua can be considered royalty in the Crystal Kingdom, she lacks the royal attitude others tend to get. The details about what her cutie mark represents have to be explained later, as they would "spoil" some things.

Her hobbies include helping others with tasks, singing, and the thing she did to earn her cutie mark.

Edit: Completely forgot her glow effect.