Compounds that are valuable as solid lubricants are the disulfides, diselenides and tellurides of tungsten, molybdenum, niobium and tantalum. Of these, only molybdenum disulfide is a naturally occurring compound, while other dichalcogenides are synthetic. MOS2 is also a widely used and representative compound lubricant. Another representative one is tungsten disulfide. When molybdenum disulfide is limited