Not all bitcoins are created equal in the eyes of institutional investors, according to “Shark Tank” star Kevin O’Leary.

Institutions want greater transparency about where and how bitcoin is mined, raising the prospect that only some of the supply will end up in Wall Street custody, O’Leary said Monday on CoinDesk TV’s “First Mover.”

Also known as “Mr Wonderful,” O’Leary has changed his mind about bitcoin as an asset class, now weighting BTC at 3% of his personal portfolio. But he said he doesn’t want to buy bitcoin mined in a way that causes energy waste and environmental damage. 

“I want to make sure my coin is mined efficiently,” he said, comparing dirty bitcoin to “blood diamonds” that finance unsavory activities in the developing world. Such desire among investors could preclude buying bitcoin mined in China, for instance, which is known for powering its mining with coal-derived electricity (though also hydroelectric plants during the rainy season).

O’Leary’s comments suggest the recent influx of traditional investors to the bitcoin market could revive an old debate, though for new reasons.

For years, there has been talk of newly mined, “virgin” bitcoins fetching a premium over units that have passed through multiple wallets. Supposedly, buyers wanted to avoid any taint from coins that may have been used in illicit darknet marketplaces.

If true, this would mean bitcoin is not truly fungible, or interchangeable, meaning it lacks one of the fundamental properties of money. However, evidence of virgin bitcoin premium has been largely anecdotal, and many market participants have called the idea dubious. 

If O’Leary is right, however, Wall Street’s environmental conscience – or at least, its desire to project one – could lead to a new differentiation between supposedly fungible coins.

The founder of a mutual fund company, a venture capital firm and an exchange-traded fund (ETF), O’Leary noted that many institutions have two committees deciding on asset allocations these days: an investment committee and a sustainability committee. 

Bitcoin needs to satisfy stakeholders on both before companies are going to jump in, he argued.

“I don’t think the community realizes how big this issue is going to become,” he said. 

O’Leary said he plans to be active in the mining space, partnering with miners that want to reduce their carbon footprint. 

He predicted that some institutions may want to mine their own BTC so as to assure provenance for their clients.

According to O’Leary, only 10% of people at financial institutions who want to invest in the premier cryptocurrency have done so yet, suggesting big unmet demand and rising future prices. 

Read more: The Frustrating, Maddening, All-Consuming Bitcoin Energy Debate