Hornfels, a fine-grained, metamorphic rock is a very hard rock that is very durable. It contains the mineral mica, and is usually dark-brown, to black in color. It is formed by contact metamorphism due to heat on shale or mudstone. It is used in the construction and roading industries. It is used as a road base and in concrete. It can be used in landscaping applications as decorative rock in gardens. In prehistoric times, people fashioned tools from hornfels. These were used for butchering game, and for such objects as scrapers and knives.
In prehistoric times, hornfels was used to make simple tools such as knives, scrapers, and arrowheads.
Nowadays it is used primarily as an aggregate in paving and construction or as a decorative stone.