Which stones in nature can be used as grindstones?

1. Sandstone is a kind of sedimentary rock, which is consolidated by water scouring stone particles deposited on the river bed after thousands of years of accumulation. Later, due to the earth's orogeny, today's mines were formed.

2. Main components: a. It should be more than 65% B, clay about 10% C, needle, iron, ore about13% d. Other substances are more than 10%.

3, material selection: any sandstone can be sharpened-gray clay sandstone may be the best. The timing is not bad, but it is rare. Granite can also be used. Take two pieces and smooth them with each other. The ideal sheet is smooth and rough, and can be put in a small pocket on the front of the scabbard at ordinary times. Grind the roll mouth with a flaky rough surface to get a shiny surface. The key is that the grinded blade must be sharp and durable, and it is not easy to produce nicks.