DairyNZ's general manager farm performance, Vanessa Winning, says she was touched by the Becketts' appreciation for dairy farmers.
"This is such a thoughtful gift, a true surprise and delight for farmers," she said.
"While we receive praise and recognition for the work our farmers and their teams are doing on farm and in their surrounding communities, this is the first time anyone has expressed their admiration and thanks in this way."
The Becketts both come from dairy farming families. He was raised on a dairy farm in Matamata, while as a child she often visited her grandparents' dairy farm, now part of Auckland airport.
"Even back then, our farming families had a long-term view of environmental stewardship. Everything my father did on the farm was to care for the land and his animals," Mr Beckett said.
"It's my opinion that dairy farmers are more environmentally green than most, certainly greener than many non-farming people, because of the work they do to protect the environment.
"We see some dairy farmers getting bad press for allegedly stuffing up the streams and their cows get the blame for global warming. We saw the opportunity to give away this appropriately green-coloured diamond to thank the good farmers for their hard work, both as stewards of the land and also in bringing us milk."
In his decades as a jeweller, he had only once before had a green diamond. He came across the one he is giving away in a collection of estate jewellery in Australia, where it had been part of a family collection for several generations. The most famous specimen was the Dresden green diamond, found in India two centuries ago, and is named after the German city where it is on display.