A coal deposit is a natural accumulation of coal in the Earth's crust. It is typically composed of seams, veins, SILT, lodes, and loess. A SEAM is a layer of coal that is usually several feet thick and can be mined. A VEIN is a narrow band of coal that is found within a SEAM. SILT is a fine-grained sedimentary material that is often found in coal deposits. A LODE is a mineral deposit that is formed within a fissure or crack in the Earth's crust. Loess is a type of sedimentary material that is composed of wind-blown dust and is often found in coal deposits.