Fine oyster sea shell, 20 Pound. This is the same fine gravel I use it as substitution for Dyna rock, I'm using this oyster shell for years with the best results for all my seedlings as showed on my seedling kit for sale, using oyster shell as top layer for seedlings avoid fungus keeping the top dry and clean, I use it also for mixing a special blend to plant a very valuable plants like lophophoras, aztekium, pelecyphora, ariocarpus, lithops, rare mesembs, or any plant that need a very good drained soil. For every item you add in quantity will be 1 item equal to 20 pound