I am an herbalist as well as a gardener. To me buying oyster shell is just a waste of my money when it is cheaper to grow something as good or better. I know for many they perfer to grow what they can for feeding thier chickens. Since calcium is such a big thing I thought I would list some plants that are high in calcium that are easy to grow. All of these have other high vitiamins and minerals also. Here is a list with numbers included. 3 1/2 ounce (2 to3 cups) Arugula 309 mg Turnip Greens 190 mg dandelion greens 187mg kale 135 mg watercress 120 mg beet greens 119 mg collards 117 mg mustard greens 103 mg chicory(curly endive) 100 mg The reasource I am pulling this infomation from is from the University of California at Berkeley book they wrote call The Wellness Encyclopedia of Food and Nutrition. It covers alot of food and list numbers aross the vit and min board. So if anyone would like to know the nutritional facts on one type of food just Pm me I would be glad to answer. This is for human type food only so things like feed corn would not be included but wheat, bran rice and sweet corn is for example. The lists in this reasource include veggis,fruits,exotic veggis and fruits, grains and grain products, legumes,nuts, seeds, meat, poultry, fish,shellfish, dairy and eggs. Nothing like having another source for something instead of just one product. Hope you all enjoy.