Natural Science in Archaeology

Chapter 10
Abrasives, Salt, Shells, and Miscellaneous
Geologic Raw Materials
10.1 Introduction
This chapter contains reviews and discussions of geologic raw materials that did not
fit conveniently into the systematics of the other chapters.
10.2 Abrasives
Since ancient times, many rocks and minerals have been used as abrasives, including
emery, pumice, diatomite, feldspar, quartz minerals, and various metal oxides. Abrasives
must be both hard and cohesive, i.e., not subject to easy fracturing. Throughout
the ancient world, quartz (hardness of 7) was undoubtedly the most common
abrasive. It was available nearly everywhere either as quartz sand or crushed quartz.
By about 3500 BCE engravers were using quartz powder to engrave cylinder seals.
It appears that emery powder came into use by the second millennium. One of the
first major uses of abrasive grit was in the construction of the pyramids of Egypt
where the surfaces of stone blocks were rubbed smooth for a remarkably good fit.
The creation of ground stone objects requires an abrasive material. Flaked axes
with ground edges are found in Japan and northern Australia dated earlier than
10,000 years BP. By the ninth millennium BP, flaked axes appeared in northwestern
Europe and southwestern Asia (Bordaz 1970). Quartz sandstones used as grinders
also appeared at this time. Grindstone artifacts appeared in Egypt and Mesopotamia
around 2000 BCE, in China around 1500 BCE, in Greece before 700 BCE, and in
central Europe about 500 CE (Pinkstone 1974).
One useful abrasive is emery, which is a naturally occurring aggregate of corundum
(Al 2 O 3 ) and magnetite (Fe 3 O 4 ), sometimes with spinel [(Mg,Fe)Al 2 O 4 ] or sillimanite
(Al 2 SiO 5 ). Some emery contains plagioclase. The hardness and abrasive or
cutting quality of emery depend on the amount of corundum present. Corundum has
a hardness of 9 and is exceptionally cohesive and durable. Hence, emery deposits
that are high in corundum make exceedingly good abrasives. The hardness of magnetite
is 5.5–6.5; that of spinel is 7.5–8; and that of sillimanite is 6.5–7.5. The emery
G. Rapp, Archaeomineralogy, 2nd ed., Natural Science in Archaeology,
DOI 10.1007/978-3-540-78594-1_10, © Springer-Verlag Berlin Heidelberg 2009
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