アンタークチサイト, Antarc

Hardness level is 3. Antarcticite is one of the Gems who mainly does patrol duty and some other work specifically in winter. Due to their gem characteristic, they 'sleep' in liquid form during above room-temperature, and re-crystallize when the temperature drops. The colder the temperature, the harder they become.
A perfectionist and quite formal (as well as somewhat apathetic), but also spoiled towards Adamant-sensei. They love to hug them, but are embarrassed when anyone finds out.

Antarc is very blunt, and judgmental, but deep down is emotional and kind. But, after hearing Phos' story, they let them become their partner, though they are not used to working in a group.