Hammerstone

In archaeology, a hammerstone is a hard cobble used to strike off lithic flakes from a lump of tool stone during the process of lithic reduction. The hammerstone is a rather universal stone tool which appeared early in most regions of the world including Europe, India and North America. This technology was of major importance to prehistoric cultures before the age of metalworking.

A hammerstone is made of a material such as sandstone, limestone or quartzite, is often ovoid in shape (to better fit the human hand), and develops telltale battering marks on one or both ends. In archaeological recovery, hammerstones are often found in association with other stone tool artifacts, debitage and/or objects of the hammer such as ore. The modern use of hammerstones is now mostly limited to flintknappers and others who wish to develop a better understanding of how stone tools were made.

Hammerstones are or were used to produce flakes and hand axes as well as more specialist tools from materials such as flint and chert. They were applied to the edges of such stones so that the impact forces caused brittle fractures, and loss of flakes for example. They were also widely used to reduce the bulk of other hard stones such as jade, jadeite and hornstone to make polished stone tools. A good example is the hornstone found in the English Lake District used to make polished axes during the early Neolithic period, and known as the Langdale axe industry.

...
Wikipedia