Bitcoin is a market for criminals and millennials, Dennis Gartman says

• Analysts expect bitcoin's value will surge again following a recent dramatic decline, but bitcoin bear Dennis Gartman said he still will not invest in it.
• "This is a market ... for criminals, this is a market for millennials," the commodities guru told CNBC's "Fast Money."

Commodities guru Dennis Gartman is not backing off his dramatically bearish stance on bitcoin.

"This is a market ... for criminals, this is a market for millennials," Gartman told CNBC's "Fast Money" on Monday. "This is a market for pure punters, but there is no value here whatsoever."

Even the cryptocurrency's tendency to bounce back in a big way from steep declines is not swaying Gartman.

"How can you buy or sell a painting using bitcoin, when the change in volatility is 20-30-40 percent in the course of a week? It's nonsense," he said. "I shall not trade it."

Bitcoin fell about 20 percent over the weekend, but regained much of its losses. Historically, the cryptocurrency has gained about 28 percent in the weeks following a drop of 20 percent or more.

Monday marked yet another instance of Gartman trashing the cryptocurrency. In August, he told "Fast Money" that he "didn't understand it to begin with, don't understand it now."

Gartman added that he appreciates cryptocurrency's use of blockchain technology, but he believes there are better uses for blockchain.

"There's no question blockchain has merit. It's going to change the manner in which we trade. It's going to change the manner in which we invest," Gartman said.