Prices for NFTs have skyrocketed this summer, and crypto enthusiasts have invested exorbitant amounts of money in everything from digital trading cards to virtual property.

Now you can add digital rocks to the mix as well.

Prices doubled over the weekend and then again on Monday for EtherRocks, an early NFT project consisting of identical digital rocks that come in different colors, with some selling for more than 69 Ether, according to the Twitteraccount @EtherRockPrice, which tracks the rocks’ prices.

This means some rocks are selling for more than $200,000, and the price floor is more than $100,000 based on the price of Ether as of publication. Three days ago, the rocks were selling for around $50,000.

Although NFTs have been around for years, they exploded in popularity earlier this year during the pandemic and following the $69.3 million sale of an NFT collage at Christie’s by digital artist Beeple.

NFTs can be purchased on different third-party exchanges, one of the most popular of which is OpenSea.io. As for the EtherRocks, they can only be purchased on the project’s website.

The NFT rocks have been around since 2017, and were created around the same time as CryptoPunks, one of the earliest NFTs on the Ethereum blockchain.

On the EtherRocks website it states that the NFTs “serve NO PURPOSE beyond being able to be brought [sic] and sold, and giving you a strong sense of pride in being an owner of 1 of the only 100 rocks in the game :).”

Some of these 100 EtherRocks have been lost over time, according to CryptoBriefing, and the limited quantity has caused the price of the rocks to soar. Collectors are especially keen on rocks of different hues, including four rare bluish rocks, which contrast with the gray shades of most of the others.

One owner of a bluish NFT rock, who goes by @LilMoonLambo on Twitter, has listed it for 500 ETH, or more than $1 million. The rock has not yet sold.

They said they purchased the rock because in their opinion it is the second best historical NFT behind Larva Labs’ CryptoPunks.

“We live in the meme economy, and right now jpeg rocks are outperforming gold,” they told Fortune via Twitter DM. “Digital scarcity is the trend in a world of inflation.”

LilMoonLambo said the rocks have more value because of the scarcity compared with the CryptoPunks NFTs, of which there are thousands in existence.

“500 ETH is a drop in the bucket in the crypto art space,” they said.