Natural Science in Archaeology

5.3 Non-Quartz Silicates and Minerals 103
Predynastic times (Lucas 1989). It appeared in ancient Greece and Rome after Alexander
the Great’s conquest of the East (Spier 1989). Medieval Arab traders procured
garnets ( acqeeq aahmar) from Afghanistan (Sersen 1995). Garnets were
also found in Sri Lanka, India, Bohemia, and Burma (Bauer 1968). The Romans
sometimes hollowed out the underside of the garnets to make them more transparent
(Bauer 1968). Almandine was used as a gemstone and for beads.
Pyrope garnet of the rhodolite variety Mg 3 Al 2 (SiO 4 ) 3 , is pinkish-red, purplishred,
orange-red, or crimson to nearly black in color. Its name is derived from the
Greek word for “fiery.” Pliny refers to red stones by the general term carbunculus.
He lists sources as India, North Africa, Caria, Ethiopia, Miletus, Orchomenos,
Chios, Corinth, Troezen, Marseilles, and Lisbon (N.H. 37.91, 92–98, 103, 122,
123). His description may have included pyrope. However, pyrope garnet is found
only in the foothills of the Central Mountains in Bohemia. Mining of Bohemian
garnet is reported by Agricola. Pliny also mentions a fiery red to purple stone called
lychnis which came from Orthosia and Caria (N.H. 37.103, 104). Garnets were used
primarily as gemstones.
Sodalite, Na 4 Al 3 Si3O 12 Cl has a hardness of 5.5–6 and a density that varies from
2.14–2.4. Its name comes from the sodium in the mineral composition. Annersten
and Hassib (1979) attribute the blue color of sodalite to the presence of colloidal
particles of metallic sodium. This gemstone is usually blue, but may be colorless
or appear in white, pink, yellowish, greenish, or reddish varieties. Pink sodalite
usually fades when exposed to visible light. Hackmanite is a variety of sodalite.
Sodalite forms in silica-poor granitic rocks and in some metamorphosed calcareous
rocks. It is found in Germany, Romania, Burma, and Korea.
Feldspars. The feldspars are Na, Ca, K, and Al silicates with a hardness varying
from 6 to 6.5 and densities from 2.55 to 2.76. The name comes from the Swedish
for field plus spar in reference to finding feldspar in fields overlying granite. The
feldspars are the most common minerals in the earth’s crust and are major constituents
of most igneous rocks. Feldspars are generally dull, cloudy and fairly opaque
so they have not been widely sought after as ornamental “stones”. They have, however,
been found in archaeological contexts (Dittert 1968). The common feldspars
are orthoclase, plagioclase, and microcline. Semiprecious stone varieties of feldspar
include sunstone, moonstone and amazonstone. Indigenous Americans used
all as gems: moonstone was used in Mexico, sunstone was used by the Apaches in
Arizona, and amazonstone was used by the Aztecs, Mayas, Indians of Venezuela,
Brazil, Trinidad, Wisconsin, and California.
Labradorite/Sunstone is named after its principal locality on the coast of Labrador.
Labradorite can be colorless, white, or gray, and frequently exhibits an iridescent
play of colors. Sunstone contains inclusions of hematite in parallel minute
plate-like inclusions, giving it a spangled appearance.
Microcline feldspar varieties include amazonstone (amazonite), which is usually
green, and perthite, which can be white, gray, yellowish, reddish, or green in
color. The color is due to the presence of Pb 2+ and OH – . The name micrcline comes
from Greek, meaning little slanted, which refers to the cleavage angle. The name
plagioclase comes from the Greek for oblique fracture.