Natural Science in Archaeology

78 4 Lithic Materials
In a highly recommended comprehensive monograph on chert and flint, archaeologist
B.E. Luedtke (1992) opts for using chert as the general term for all rocks
composed primarily of microcrystalline quartz. This book takes a slightly different
approach. For example, chalcedony is distinguished from chert because it has a different
fibrous structure that is easy to recognize under the petrographic microscope.
However, chert often contains chalcedony.
In many limestones (and dolomites) silica is segregated into chert (or flint) nodules.
These nodular masses vary from small disks a few centimeters across to much
larger flat or tubular bodies. In most limestones, including the Cretaceous chalks of
England and France, the nodules are elongated and concentrated parallel to certain
bedding planes. Although most chert nodules are fine-grained, dense silica, some
contain calcareous fossils, other carbonates, and iron oxide. Several types of fossils
may be present in cherts, and carbonized plant fragments are not uncommon.
The author has noted many lithics made from oolitic cherts. In some, the oolites are
clearly outlined, and their nuclei are often fragments of bryozoans. Occasionally,
the oolites are composed of the same cryptocrystalline silica as the cement, and they
almost disappear under crossed nicols in a polarizing microscope. Cherts may have
the texture and fracture of unglazed porcelain. In Europe important chert deposits
occur in southern Scotland, south Wales, southeastern England, and the radiolarian
cherts of the Alps and Apennines (Weisgerber 1999).
Siderite (FeCO 3 ) can occur intimately interbedded with cherty iron carbonates, clay
ironstones, and iron oxides. In the Lake Superior region of North America, these rocks
are thick and widespread and produce occurrences of jasper that provided good lithic
material for early societies in the region. Chert occurs as bedded deposits, discontinuous
lenses and nodules usually interstratified with chalk, limestone or dolomite.
A well-known American geologist in the middle 1900s, Kirk Bryan (1950), presented
a broad discussion of “flint” quarries and tool manufacture. He began with a
historical look, referring to the work of W.H. Holmes in the 1890s on lithic (quartzite)
production. In describing a lithic quarry about 50 km northwest of Amarillo, Texas,
Bryan called the chalcedony recovered from a dolomite formation a flint. Although
Bryan was a geomorphologist and Quaternary geologist, this paper is largely about
manufacturing technique.
Chert can be almost any color and can accommodate a wide variety of impurities
that affect its workability in lithic manufacture. Carbonaceous cherts are frequently
dark in color with a fair conchoidal structure and a vitreous luster. Their color is
often attributed to a high content of organic matter, but this is not always true. One
type of carbonaceous chert (called silexites in French) is very impure and develops
in fossiliferous, coarse-grained clastic limestones. The very fine-grained, very
dark-colored nodules found in chalk deposits represent a second type of carbonaceous
chert. These are the classic flints.
Chert and related stone procurement areas and workshops are known throughout
the ancient world. Some examples from Central and North America are described in
Anderson (1978), Shafer and Hester (1983), Butler and May (1984), Ericson and Purdy
(1984), Hester and Shafer (1984), Green (1985), Vehick (1985), Justice (1987), Sanders
(1990), Arnold (1992), Gramly (1992b), Morrow et al. (1992), and Low (1996). An