Chert is a very fine-grained sedimentary rock that is primarily composed of microcrystalline quartz. It is formed from the precipitation of silica from groundwater or surface water, and is often found in association with other sedimentary rocks such as limestone and shale. Chert typically has a dark, almost black colour, but can also be found in various shades of grey, brown, red, and green. Its texture is typically very fine-grained and homogeneous, with a conchoidal fracture and a dull lustre. The fracture surfaces of chert are often sharp and splintery, and the rock may break with a brittle, snapping sound. Chert is a very hard rock, with a Mohs hardness of 7, and is resistant to weathering and erosion. Due to its hardness and durability, it has been used throughout history for the production of tools, weapons, and other objects.