Mineral oil/petrolatum (they're the same thing) and cones are used in skincare products to help you retain moisture. They do just lie on top of your skin, but they form a barrier by doing that. I find that having this "barrier" isn't enough, and some kind of humectant (like glycerin) or softener (like jojoba) is also needed. I think a good moisturizer would have petrolatum or a cone, plus a plant-derived substance, in the first 5 ingredients.