A boondie is an Australian term for a sand cake that is carved from, or broken off of, a larger, hardened pocket of sand. Boondies are typically yellow-orange in colour due to a coating of iron-oxide. It is this iron oxide that causes the quartz grains to stick together. Boodies are intended to be thrown like snow balls. They are less dangerous than rocks, since they disintegrate on impact.
Boondie may come from 'boundie'. An African term for that is like a rock but not.
I threw a sand boondie at Johnny. You should've seen it explode.
When you piss in the sand and it creates a sand boondie made out of piss. One could say a yellow snow ball
Kyle: "Shit Damo.. that one hurt like a bastard.. you caught me square in me mouth mate.."
Damo: "Yeah, it probably tasted a bit funky too bro, it was a piss boondie"