A layer of ore is a type of mineral deposit that is found in the Earth's crust. It is usually composed of a variety of minerals and metals, and can be mined for commercial use. The term 'layer of ore' can refer to a SEAM, which is a thin layer of ore that is found between two other layers of rock, or a VEIN, which is a thicker layer of ore that is found within a larger mass of rock. A topslice is a layer of ore that is found at the top of a mineral deposit.