The latest craze to resurface in the effervescent nonfungible token (NFT) scene is a collection of digital pet rocks from 2017 dubbed EtherRocks.

On Sunday, a single EtherRock sold for a whopping 45 Ether (ETH) — worth roughly $135,240 at the time.

EtherRock was one of the first crypto collectible NFTs issued on the Ethereum blockchain, following shortly after CryptoPunks’ June 2017 launch. Every EtherRock showcases a still image of a stone, with each token donning a unique color but being identical in shape and size.

Only 100 EtherRocks will ever be minted, with the project’s smart contracts having been deployed on Dec. 25, 2017. According to Etherscan, the first EtherRock appears to have been sold on Dec. 26, 2017, for 0.099 ETH (worth roughly $300 at the time).

Etherscan shows that only about 20 more rocks were sold in the first three years of the game’s existence, fetching prices between 0.1 and 0.36 ETH. After slow but steady sales during the first half of 2021, the recently bubbling NFT market has inspired investors to rush the remaining EtherRock supply — causing prices to surge.

With each of the 100 EtherRocks having sold off, many of the tokens have been put up for resale on popular NFT marketplaces. Secondary prices range from 31 ETH ($96,100) up to a staggering 626,262 ETH (roughly $1.9 billion).

Physical pet rocks were first launched back in 1975 as a collectible toy by advertising executive Gary Dahl.

Related: Tales from 2050: A look into a world built on NFTs

Offering tongue-in-cheek comment on the surging popularity of the tokenized pet rocks, Ran Neuner, co-founder and CEO of Onchain Capital, tweeted on Tuesday that the NFTs are the ultimate store of value and inflation hedge:

“There are 7bn people in the world, 21m Bitcoin — But only 100 Rocks in the world. Can you imagine what happens when institutional money starts flowing into rocks? It’s a matter of time until a Rocks ETF is approved.”

CryptoPunks have been one of the biggest successes in the world of NFT collecting, with the tokens regularly fetching six-figure prices. As reported by Cointelegraph on Wednesday, a crafty collector recently made $80,000 profit in a CryptoPunk resale after purchasing the token for virtually nothing.