Natural Science in Archaeology

118 5 Gemstones, Seal Stones, and Ceremonial Stones
Coal. Coal is an organic sedimentary rock resulting from the accumulation of plant
material. Beds of hard coal have closely spaced vertical jointing known as “cleat,”
with a less-developed jointing at right angles and a hardness between 3 and 4. The
varieties of coal called cannel coal and jet were used for gemstones and decorative
artifacts. The color varies from brownish-black to deep velvety black. There is solid
evidence that humans used coal os a fuel as far back as 30,000 BP at a Paleolithic site
in Silesia where coal outcrops at the surface near the site (Klíama 1956).
Jet was just one of a range of black lithic materials used in ancient times for
jewelry. Jet is a lustrous black substance that is easily worked and will take a high
polish. Jet has sometimes been called Black Amber. Like amber, it sometimes was
burned and the fumes inhaled to alleviate edema, colds, female disorders, and hysteria.
Hunter et al. (1993) investigated a wide range of analytical techniques and recommended
techniques including Fourier transform infrared (FTIR) spectroscopy
and X-radiography to resolve questions of identification. The word “jet” is taken
from Greek gagates (Gagas), a town and river of Lycia in Asia Minor. According
to Pliny, jet was procured from Pamphylia and Lycia (N.H. 36.141–142). There
appears to have been a marked increase in the use of jet-like materials in the last few
centuries of the third millennium BCE (Sheridan and Davis 2002).
Jet occurs as sporadic lenticular masses and is “derived from pieces of drifted
wood buried in isolation which did not pass through a peat phase and thus were
not coalified, but underwent decomposition and retained their cellular structure”
(Ashurst and Dimes 1998). Cannel is from Scots dialect for “candle” (Ashurst and
Dimes 1998). Deposits found in England have been exploited since prehistoric
times, especially the Bronze Age (Shepherd 1981). The earliest use of jet in the
British Isles dates to the first half of the 4th millennium BCE. Britain’s only significant
source of quality jet is at Whitby in North Yorkshire. The other European
deposits of importance are in the Asturias in northern Spain, in the Poseidon slate
of the Swabian and Frankish Alps in Germany, in the Upper Chalk formations of
southern France, on the Dutch island of Bornholm, and in Poland. Lesser deposits
have been found in the Czech Republic, Slovakia, Italy, and Portugal, as well as
in Canada, the USA, India and Russia. (Muller 1980) Jet beads have been found
in female burials of the Iron Age in the southern Ural Mountains (Morgunova and
Khokhlova 2006).
Lignite, Kimmeridge coal, black shale, and cannel coal have all been erroneously
called jet. Distinguishing between jet, cannel coal, lignite, and torbanite can
be very difficult, and special analytical techniques may be required (Watts and
Pollard 1999). Cannel coal is dense, lusterless, blackish, and typically shows conchoidal
fracture surfaces. It is composed largely of spore and pollen remains, resin,
and fragmented leaf cuticles (Ashurst and Dimes 1998). As a gemstone, hard coal
was used mainly for beads and small, carved objects. Coal is more rarely found as
larger, carved objects such as the Coal Seat at Osborne House in the Isle of Wight,
and there is at least one example of the use of cannel coal as decorative inlay in the
floor of Lichfield Cathedral in Britain (Ashurst and Dimes 1998).
In the second millennium BCE, jet from the great deposit at Whitby in the British
Isles was traded far and wide. Jet amulets have been recovered in a third century