If I had to be a non-emerald gem...
Gem: Star sapphire (not the Isidar Mithrim, that's more a star ruby anyway)
Color: navy blue
Location: right eye
Appearance: Skin is pale blue. Right eye is a blue star sapphire, covered by an eye patch when not on a mission. His left eye is a deep pure blue. Typically wears a navy hoodie over a blue shirt and tight jeans with blue shoes. Eyepatch has a triangle pattern on the outside, and a detailed picture of the Aesir on the inside.
Other info: His weapon is throwing stars, summoned by channeling his faith in the Norse pantheon-a devout worshipper, but do not call him neopagan. He's been around long enough to stop Thor's Oak from being cut down and watched the tree die of old age- through his gem. He leads a group of two other gems from a temple located at the conjunction of the White, Blue, and main Nile rivers, outside the city of Khartoum. The trio each represent a major pantheon: Kemetic (Egypt's gods), Olympian, and Aesir.