Strictly speaking, there is no jade to be found in New Zealand; it's virtually all nephrite, which is a blend of actinolite and tremolite or Ca2(Mg, Fe)5Si8O22(OH)2 (my face is as blank as yours right now). To cut a very long geological story short, nephrite starts life as something igneous or metamorphic, often at altitude, and ends up as a gnarly and almost completely anonymous boulder in the middle of a river on the West Coast of the South Island, the latter designated Te Wai Pounamu by Maori as an acknowledgement. The boulders are both prospected by local tribes and poached by irresponsible douchebags, typically with heavy machinery, though some blocks are sectioned with diamond saws in situ due to their great weight. The 'greenstone' sold to unsuspecting tourists at the many tacky outlets infesting this fair land is often Chinese rubbish and I would encourage you not to buy it. If you're looking for a souvenir, think about patronizing one of the many local carvers using NZ nephrite. Just ask around.
Though I've always loved greenstone it can be a difficult wear, sharing an intimate, almost tender affinity with the right person but visibly militating against a less sympathetic companion. Time will tell if this pendant decides I'm cut from the right cloth. I certainly hope so.