Plant it to grow Cloudstone Block. Cloudstone is very rare, because it tends to fall out of the sky and just become Stonestone.
Cloudstone Block Seed price in Growtopia: sells for about 1 WL, buyers pay about 2 WL (median of 4 offers from community Discords, past 30 days). Live price chart and the latest buy and sell offers.
Recently sold at: 64CR