Page 31 - visitorGuide

■ Native Sulfur with Celestite
This specimen comes from Sicily, where fine crystals of native sulfur (yellow)
occur in association with celestite and other minerals. Native sulfur is a minor
ore of sulfur, and celestite is the principal ore of strontium. Strontium is used
to make specialty glass, glaze, enamel, caustic soda, and in the processing
of sugar beets. It is also used in strontium nitrate, which produces the bright
crimson flame in fireworks and signal flares. Strontium is also used in batter-
ies, paints, rubber, waxes, refrigerant solutions, and pharmaceuticals.

Gift from the Department of Geology, University of Tennessee, Knoxville, through Otto C. Kopp.

■ Agate Slab
This slab of agate, polished on both sides, is from Brazil. Fluids rich in dis-
solved silica filled a cavity in basalt rocks and left behind this agate.The hori-
zontally layered, fine-grained silica was deposited layer-by-layer from solu-
tion.The crystalline quartz filled the remainder of the cavity later.

Purchased by the Society.

Wind-Sculpted ■ Wind-Sculpted Boulder of Chert and Dolomite
Boulder The alternating layers of darker chert and light dolomite
were worn down by wind-blown sand, silt, and mois-
ture. Chert is more resistant to weathering, so the chert

layers stand out as polished ridges. Dolomite is more
soluble and less resistant to weathering; it forms the
indented layers.

■ Spodumene Crystal
This crystal, from Minas Gerais, Brazil, is of gem-
quality spodumene. Spodumene is characterized
by long, flat crystals with deep, lengthwise grooves
and an uneven, splintery surface. The sharply de-
fined change in color near the center of the crys-
tal is especially rare. Spodumene occurs in white
to green prismatic crystals, often of great size. It
takes its name from the Greek spodumenos (“burned
to ash”) in reference to the ashy-colored, woodlike appear-
ance of its weathered surfaces.The pink gem variety is known
as kunzite, after G.F. Kunz, a noted American gemologist.

Gift from Raymond M. Thompson, Englewood, Colorado.

■ Fossil Brachiopod
Brachiopods have lived since the early Paleozoic. Although most forms are
extinct, one branch has survived to modern times. Brachiopods were at their
peak during the middle and late Paleozoic, about the time this brachiopod
was alive. They lived attached to rocks, shells, or other hard surfaces at the
bottom of the sea.

Gift from Xu Zheng-Liang, East China Geological Institute.

■ Tourmaline-Cemented Breccia
This unusual breccia, from the Cananea mining district in Sonora, Mexico,
forms a ring around a copper and silver ore body. It contains fragments of
volcanic rhyolite and igneous quartz monzonite porphyry, all cemented by
black tourmaline.The feldspar-bearing rock fragments are veined by quartz.

Gift from Compañía Minera de Cananea, S.A. de C.V., courtesy of Guillermo A. Salas, Cananea, Mexico.

21GARDEN LEVEL EXHIBITS