By growing pineapples inside cubical molds, they can be forced to grow in a block shape! There's no real reason to do this, but it is fun.
Pineapple Block price in Growtopia: sells for about 5/WL (median of 67 offers from community Discords, past 30 days). Live price chart and the latest buy and sell offers.
Recently sold at: KONOO, THENASTUFF, WLJF