Shares of major crypto exchange Coinbase (COIN) changed hands at a roughly $90B value last week, according to a fresh report from Bloomberg. It's an astounding valuation given that the company was appraised at $8B in October 2018. The valuation is based on $350 a share, the price the stock was trading on the Nasdaq Private Market on Thursday. The auction was the last before Coinbase goes public in late March, though private trading is usually more restrictive and volumes are smaller, so it's not a perfect picture of a company's value.Backdrop: Coinbase started operations in 2012 and operates one of the largest digital currency exchanges. The bulk of its revenue comes from trading fees, though it also launched the Coinbase Index Fund in 2018, which is available only to accredited investors (defined as those with an annual income of $200K or a net worth of $1M or more). Going