Different Rocks to Make Stone Knives

Several types of rock can be fashioned into a stone knife.

During the history of man, before metalworking became common, rock was the material of choice to make sharp-edged tools. Certain types of rock, specifically, those made of silica, were especially suited for fashioning into arrowheads, spear points and stone knives. The fine texture and conchoidal fracture characteristics of these rocks allows them to be shaped, or knapped, little by little, by knocking flakes of stone away to form the implement while still leaving a sharp edge on the blade.

Obsidian

Obsidian is a type of black volcanic rock, formed when silica-based rock melts and is then ejected from the volcano as liquid lava. When the rock cools, it forms a type of naturally occurring glass. This glass lacks any crystalline structure at all and fractures easily, leaving razor-sharp edges. Obsidian is among the most favored of rocks among flint knappers. The rock is extremely fragile and must be handled very carefully to prevent the stone from breaking inadvertently when being struck to remove flakes.

Flint and Chert

Flint, and the closely related rock, chert, are forms of microcrystalline quartz. The two rocks are so similar they are difficult to differentiate. Typically found in limestone deposits, flint and chert form in nodules. These nodules provide quality core material for a variety of knapping projects, including making stone knives. The fine texture of these rocks makes them a good choice for knapping. Flint and chert tend to fracture more flatly and with less of the typical conchoidal waviness of obsidian fractures.

Other Metamorphic Silicate Rocks

These rocks include agate, chalcedony, jasper, opal and quartz. Some have crystalline structures even finer than that of flint or chert and flake easily to produce slender stone knives with clean lines and extremely sharp edges. Quartz is typically a poor choice for a knapping stone, as its crystalline structure is relatively course. Large, pure crystals of quartz, however, can be used to make stone knives.

Andesite

Andesite is another form of igneous rock found around volcanic sites, similar to obsidian. The stone is more coarse in texture than obsidian, flint or chert. While this can make andesite more challenging to work, it still has a fine enough crystalline structure to knap easily.

References

• University of Iowa: Flintknapping
• California State University: Andesite
• Primitive Ways; California Knapping; Paul D. Campbell; 1999
• University of Texas: Chert