Chemistry Reference
In-Depth Information
Quartzite.
Quartzite
is a very compact, exceptionally hard and tough meta-
morphic rock derived from sandstone. It consists mainly of rather large crys-
tals of
quartz
(composed of silicon dioxide) naturally cemented by secondary
quartz. Most varieties of quartzite contain over 90% quartz, and in some
cases the quartz content exceeds 95% of the total weight of the stone. The
color of most quartzite is white or light yellow, but if it contains iron oxide
impurities it is red, while other metal oxide impurities may cause the rock
to display patchy color variations. Quartzite is very hard, which makes it
difficult to quarry. Nevertheless, because of its strength and resistance to
weathering, it has occasionally been used for construction, sculpting statu-
ary, and ornamentation.
During the fourteenth century B.C.E., for example, the ancient Egyptians
used quartzite for making statuary, stelae, and other constructions. Among
these is a famous group of monumental statues known by the plural name
Colossi of Memnon
, near Thebes (see Fig. 14). It is known that one of the
Colossi was damaged in antiquity and repaired during Roman times by
order of the emperor Septimus Severus. The
provenance
of the quartzite from
which the Colossi of Memnon were made was studied using neutron acti-
vation analysis to analyze samples removed from the sculptures as well as
from a number of quartzite sources from different geographic sites. Com-
paring the analytical results revealed that the quartzite used to make the
statues most probably originated from a quarry quite a distance away from
the location of the sculptures: almost 700 km down the Nile from Thebes.
The quartzite used for the Roman repair, however, seems to have come from
quarries nearer Thebes, upstream the river Nile (Bowman et al. 1984; Heizer
et al. 1973).
Soapstone.
Soapstone
, also known as
steatite
, is a very soft metamorphic
rock that feels greasy to the touch and can be easily carved and shaped. It
consists mainly of the mineral talc (composed of hydrous magnesium sili-
cate), often mixed with small, varying amounts of
magnetite
(composed of
iron oxide), and/or
chlorite
(a complex silicate of aluminum, iron, and mag-
nesium). Large outcrops of soapstone occur in many areas on the surface of
the earth. Because of the ease with which it can be shaped, soapstone has
been widely used since prehistoric times to manufacture small articles such
as bowls, vessels, beads, and other decorative objects. It is for this reason
that identifying the provenance and the routes of trade of ancient objects
made from soapstone has been a subject of investigation since the late nine-
teenth century. Soapstone from different sources, and even from single
sources, generally has variable composition, making it rather difficult to elu-
cidate the provenance of soapstone. Some studies seem to indicate, however,
