Mottramite is often confused with Duftite, a lighter green similar looking mineral that occurs widely at Tsumeb.
The mineral is present in all three oxidation zones, often associated with Calcite. Rare psuedomorphs include Mottramite after Tennantite and Mottramite after Wulfenite.
Mottramite is considered to be at the copper end of the descloizite subgroup - Descloizite from Tsumeb is relatively difficult to distinguish from specimens originating in nearby mines.
Presented for sale here is a lovely contrast specimen - Calcite sits atop Mottramite, most likely ontop of Malachite (Unverified).