Natural Science in Archaeology

256 11 Building, Monumental, and Statuary Materials
were exploited by ancient Romans. Because of its porosity, the stone is lightweight
and is a good insulator. Tufa was used in some medieval cathedrals to fill
the spaces between the voussoirs of vaulted ceilings (Ashurst and Dimes 1998).
Called “Lapis Tiburtinus” by the Romans, travertine is a compact form of tufa.
It was used by Romans to construct the Colosseum. Travertine was employed
in the construction of monuments in Umbria, Italy, from the Etruscan Period
to the Renaissance (Petrelli et al. 2004). A light brownish travertine was one of
ancient Egypt’s most popular ornamental materials. Prolonged exposure to sunlight
bleaches this rock to nearly white because ultraviolet light destroys color
centers in the calcite that were generated by natural radioactivity in the mineral
(Harrell et al. 2007).
Onyx-marble stone is actually fine-grained calcite (Ashurst and Dimes 1998). It
is generally not used as dimensional stone, but for decorative veneers and objects.
Pure dolomite rock, composed of the mineral dolomite CaMg(CaCO 3 ) 2 , is rare.
However, the mineral dolomite frequently occurs in limestones.
Dolomites do not weather well in heavily polluted atmosphere (Ashurst and
Dimes 1998).
An interesting Devonian limestone with a deep black color has been used in
inner and outer architectural elements in historic buildings in Kracow, Poland. The
black color is caused by an admixture of bitumens and/or the alteration of pyrite.
The rock releases an odor of petroleum if struck with a hammer. The properties
of this rock – density, compressive strength, and durability under atmospheric
factors – have made it a favorite building stone.
Sandstone is a sedimentary rock formed of interlocking grains. When poorly
cemented, sandstone lacks the inherent durability of igneous rocks such as granite.
Sandstones that are well cemented by silica, calcite, or iron oxide make durable
building stone. In the past, sandstone used for dimensional stone was quarried
in much the same fashion as other building stone. In addition, stonecutters took
advantage of joints, bedding surfaces, and type of cementation. Many sandstones
exhibit layers called “bedding planes”. The orientation of the bedding planes in a
wall is particularly important since they are potential planes of weakness. Thus,
laying the bedding planes vertically may encourage exfoliation of the stone. Even
when bedding planes are laid horizontally, differential weathering tends to occur
along these layers, resulting in recessed bands. Pueblo sites of North America,
like Mesa Verde, incorporated sandstone into the natural sandstone cliffs and
grottoes.
The ancient city of Petra is located in Jordan’s Wadi Musa, a canyon eaten into
sandstone by centuries of wind and water erosion. The site is entered through a
narrow passage known as the “syk”. Evidence of occupation at Petra includes rock
shelters dating from the upper Paleolithic (10,000 BCE). However, the most famous
and elaborate buildings were carved directly into the rock by Nabatean stonemasons
in the first century CE (Fig. 11.6).
In Britain, Durham Cathedral, begun about 1093 CE, was constructed of the local
Low Main Sandstone, a fine-grained sandstone with angular quartz grains making
up 70–85% of the rock. Other mineral constituents include feldspar, muscovite, and