Ok, so after you get yourself one of these eggs from the volcano and get back home, you need to heat it up so that it hatches, then as it’s maturing it will want to eat Ambergris, then as adults they will eat meat and rocks.
I’ve found the eggs. The eggs are located inside the volcano in an amethyst cave. There are lava pools with groups of magmasaurs in them. There are small islands with craters in them, within those craters the eggs are nestled within. But be careful there are lots of magmasaurs, magma, and what look like varient rock elementals.