Natural Science in Archaeology

244 10 Abrasives, Salt, Shells, and Miscellaneous Geologic Raw Materials
to the Far East. Ibn al-Baitar of Malaga (d. 1248) mentions a substance called
“Chinese snow” that may be gunpowder. Formulas that combine saltpeter, sulfur,
and charcoal were available in Europe around the end of the thirteenth century
CE. An explosive was known to Roger Bacon (1214(?)–1294). Almost at the same
time, an Arabic source, Al-Hasan al Rammah (ca. 1280–1290), described how
these explosive devices were made. Another contemporary account is found in the
Book of Fires for the Burning of Enemies put together under the name of Marcus
Graecus. This book includes many recipes and directions for purifying saltpeter
and making gunpowder. Saltpeter was imported to Europe from India during the
later Middle Ages and also extracted from European saltpeter deposits after 1300
CE. These deposits consisted of earth from old, dry sheep stalls and stables and
from incrustations on old walls and cellars. Early saltpeter of European and Indian
origin contained chemical impurities that caused it to become useless if exposed
to a damp atmosphere.
Saltpeter is difficult to identify because it looks like many other simple salts. The
Chinese were able to identify saltpeter by the third century CE using a potassium
flame test – it burns with a violet or purple flame. The first use of saltpeter by the
Chinese was to dissolve otherwise indissoluble ores, such as cinnabar. They also
used it as a flux in metallurgical processes.
10.7.6 Epsomite (MgSO 4 · 7H 2 O, Epsom Salt)
Epsomite, also called Epsom salt, forms in a wide variety of surficial or near-surface
geologic environments. It is readily soluble. Occurrences at Epsom, Surrey, England,
and at Sedlitz and Saidschitz in Germany have long been known. The medicinal
value of epsom salt was accidentally stumbled upon in 1618 at Epsom, south of
London. A solution of epsom salt was found to be beneficial when taken internally
or used externally.
A related mineral found in desert environments is mirabilite (Glauber’s salt),
Na 2 SO 4 10H 2 O. Mirabilite has been used since antiquity as a purgative in traditional
Chinese medicine. The Chinese call it “mang xiao” and consider it to be a
treatment for constipation, sore throat, skin ulcers, and to help heal wounds. Johann
Glauber (1604–1670) isolated the compound and called it “sal mirabilis” because
of its medical properties, especially as a laxative.
Epsomite and mirabilite were mined in Salts Cave and Mammoth Cave, Kentucky,
USA, beginning about 4000 BP. The miners likely sought these minerals as a
cathartic. They also recovered gypsum for use as a pigment (Kennedy and Watson
1997). Prehistoric and historic indigenous peoples also mined epsomite in Wyandotte
Cave in southern Indiana, USA (Cande 1993). Tankersley offers evidence to
show that the mirabilite and epsomite were renewable deposits. Salts mined from
cave walls were naturally replenished by the following season. Mirabilite grows
relatively rapidly. In dry caves replenishment can take only a few months. Humidity
can stunt or even prevent the regrowth of this mineral (Tankersley 1996).