The investment category of cryptocurrencies hit a new milestone on Tuesday, one that would have been unfathomable just a couple of years ago: $100 billion in combined market capitalization.

The break above the 12-digit threshold is largely attributable to bitcoin, which is by far the largest digital currency in the still-nascent category, and which has been on a tear lately.

Bitcoin BTCUSD, +0.00% has more than tripled in 2017, according to crypto pricing site CoinDesk, and on Tuesday it rose more than 7% to $2,879.80. Earlier, it hit a record above $2,900. Those gains have brought its market cap to $46.68 billion, accounting for nearly half of the entire category.

At its current size, bitcoin has surpassed the market capitalization of such major companies as Ford Motor Co. F, -2.25% , Deere & Co. DE, +1.26% , and Delta Air Lines Inc. DAL, +2.65% . It is larger than more than two-thirds of the components of the S&P 500 SPX, +1.59% .

The swift rise in bitcoin prices have raised concerns about valuation. On Tuesday, the billionaire Mark Cuban tweeted that bitcoin prices were “in a bubble,” adding, “I just don’t know when or how much it corrects.” He also called cryptocurrencies “more religion than asset.”

Read:Here’s how blindingly fast bitcoin has been surging

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What is the future of bitcoin?

There are more than 800 cryptocurrencies, according to CoinDesk, although most of them are thinly traded and have market capitalizations under $1 million. Only eight cryptocurrencies are worth more than $1 billion.

Besides bitcoin, ethereum is the most widely used product, with a market capitalization of nearly $24 billion. Ethereum has been an even bigger gainer than bitcoin in 2017. It started the year at $7.98 per coin, and is currently trading at $261—a rise of nearly 3,200% year-to-date.

Ripple—the third-most valuable on this metric, and which is up more than 25% over the past week—recently cracked $10 billion in value.