Bitcoin drops after Musk tweet, Yellen warns it's 'extremely inefficient' - CNET

Musk tweeted Saturday that "BTC & ETH do seem high lol," referring to Bitcoin and the digital coin Ethereum.

Musk's tweet was part of a reply to a tweet from Peter Schiff, chief market strategist for brokerage firm Euro Pacific Capital, about the value of Bitcoin versus gold-backed currency. .

On Monday, Yellen spoke at the DealBook conference about Bitcoin's use for transactions, saying the amount of energy used for the process is "staggering."