Natural Science in Archaeology

60 3 Exploitation of Mineral and Rock Raw Materials
A number of slate cist graves dating to the first century BCE have been found
in southwest China along the Min River (Tong 1982). An interesting, if minor,
example of the use of slate, as well as hornfels, is for bracers, which are archer’s
wrist guards. Bracers are made of fine-grained rocks and are found in many parts
of Europe in Early Bronze Age burials (Woodward et al. 2006). Slate, even today,
is best known as a roofing material. The use of blue slate as a roofing material in
England dates back to medieval times (Jope and Dunning 1954). The hardness and
cohesion properties of slate can vary widely, depending on the silica content and the
degree of metamorphism. A large slate blade was found in Massachusetts. Its length
was over 22 cm and it measured over 7 cm at its widest point (Smith 1945).
Metamorphism contributes to making useful rock products by forming hard and
durable quartzite from friable sand. Quartzite fractures conchoidally, allowing the same
workability into sharp tools as chert and obsidian. Quartzite has been more widely used
for chipped and groundstone tools than is commonly recognized (Figs. 3.3 and 3.4).
Lower Paleolithic artifacts, from perhaps 260,000 years ago, have been recovered from
the Diring Yuriakh site on the highest terrace of the ancient course of the Lena River
in central Siberia. The oldest stratigraphic unit is composed of well-rounded gravel,
mainly quartzite. It is not surprising that most of the 4000 artifacts recovered from
excavations are cores and flakes of quartzite. Only a few were made from diabase or
other siliceous rocks. Quartzite was the rock of choice for the tools used by Woodland
Period peoples of the Appalachians to quarry and shape steatite for bowls and other
objects. Paleolithic people in the Sahara used Nubian sandstone, a quartzite, for tools.
Quartzite was also used in Pharaonic Egypt for statues and sarcophagi.
Marble can be found in thick deposits of wide areal extent that are relatively free
of cracks and easy to quarry. It takes a high polish. The chief drawback of marble is
its high susceptibility to disintegration under the action of acid rain. Even without
modern pollution, rain is acidic, because CO 2 dissolves in atmospheric water to create
a never-ending supply of carbonic acid in rain. Marble was the preferred statuary
and monumental stone of the classical world, and in Egypt it was used for vases.
Fig. 3.3 Large hafted axe,
quartzite, Boulder Lake
Reservoir, St. Louis County,
Minnesota, USA