Amegreen is a bit of an odd one! It is a mixed form of Quartz, which typically has some purple Amethyst, white Quartz, and green Quartz.
Green Quartz is often referred to as Prasiolite – there are both natural and unnatural pieces. In the case of Amegreen, it often appears to be artificially heat-treated chevron Amethyst.
Disabling the heat treatment early, or perhaps some inclusions in the mineral, have led to a green colour rather than the orange of heat-treated Citrine.