The cause of oil stone is similar to that of coal, kerosene and ground asphalt. It is also an organic matter accumulated by ancient animals and plants. The accumulation of beds is always in shallow waters of the coast, which is rich in inferior organic plants, scales, insects and other animals that are not easily recognizable. Its structure is very fine, with lime and sand inside, and its texture is tough. It is a fine-grained rock that is used for sharp objects and other metal surfaces.
Whetstone is a substance in which a natural mineral is sintered. "Oilstone" is black or brownish black. It is grayish white due to weathering when exposed to the ground. The surface does not look like oily, but when it is distilled by hot gas, the organic matter is decomposed into kerosene, hence the name. Its texture is fine and tough, and it can be used as a grinding tool. Later, strip-shaped bonded abrasives made of abrasives and binders were also referred to as whetstones.
