For several years now, Ngai Tahu have run a pilot programme to certify legitimately gathered New Zealand pounamu, and distinguish it from the imitation or illegal alternatives.
However, more than 3 tonnes of illegally harvested or stolen pounamu has been recovered by police and returned to Ngai Tahu, but it is likely that far more remains on the market.
"No doubt there will be people still trying to illegally harvest," Te Runanga o Ngai Tahu economic development leader Jymal Morgan says. "You only have to look on Trade Me, and there's still an active trade going on there.
"If that stone has not come directly from the runanga or the local communities who are mandated to harvest that stone, it's essentially stolen."
Following treaty settlements, ownership of all naturally occurring pounamu, apart from a small section of the Arahura river, was returned to Ngai Tahu in 1997.
Today, the only greenstone which is guaranteed to have been harvested and carved legally and within New Zealand comes with Ngai Tahu Certification.
This doesn't stop numerous businesses and carvers using pounamu branding to sell off cheap imitations - often labelled "New Zealand-made greenstone" or "nephrite jade".
With few legal boundaries on the advertising of pounamu, Morgan says it's "a grey and murky area".
"You don't have any assurance for anything other than Ngai Tahu pounamu that it is authentically New Zealand, sustainably harvested in a culturally appropriate manner. Essentially, you're taking the risk if you want to buy something else."
Canterbury Museum gift shop supervisor Annie Grynczyk-Shand has been involved in retail of pounamu for 12 years.
The store sells Ngai Tahu certified pounamu, alongside a range of alternatives, including some which is carved in New Zealand from imported jade, and some which is entirely manufactured offshore.
Grynczyk-Shand says over time, suppliers have become less upfront about the origins of their stone, but retailers depend on an element of trust.
"We ask questions all the time, when we're buying the product, but we are only as good as the people we buy from. We can sit one-on-one with a carver, and ask where his greenstone comes from, but we can't know from looking at a piece." Increased regulation of the stone means there is "quite a market at the moment for carvers who can't get hold of New Zealand pounamu to carve British Columbian greenstone", she says.
While labelling is often unclear, "we never guarantee to our customers or say to our customers that it's New Zealand greenstone".
In the long run, confusion around cheap imitations could hurt the whole industry, with a University of Otago study showing tourists were reluctant to buy pounamu if they could not determine its quality or provenance.
Morgan says the substitutes also hurt New Zealand artisans.
"It does impact on individual carvers and the industry, because they can't compete. Economically and commercially they can't compete with a Chinese factory carving 1000 Maori motifs an hour and sending them over here."
As well as taking an economic toll, pounamu has cultural significance for Maori.
"From a tribal perspective, we've developed a whole culture around it, our stories breathe life into the stone for us. It's not just a stone," Morgan says.
Despite the challenges, he believes awareness is growing of the importance of legitimate pounamu. "There's more questions going toward retailers. And that will encourage retailers to actually ensure they're sourcing from reputable places."
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