Page 30 - visitorGuide

■ Quartz Crystal Aggregate
Quartz is a common mineral found in many kinds of igneous, sedimentary,
and metamorphic rocks. Quartz varieties share the same chemical composi-
tion but differ widely in color, pattern, and form. Some quartz is transpar-
ent and colorless, but it also occurs in a wide range of colors produced
by impurities or defects in atomic structure. Amethyst, citrine, milky quartz
(this specimen), rose quartz, and smoky quartz are among the familiar vari-
eties. Other varieties include aventurine, a colored quartz with tiny glisten-
ing flakes of mica, iron oxide, or clay, and tiger’s-eye, a quartz variety with
chatoyant bands of yellow and brown.

Quartz is used to make glass and in optical and electronic instruments.
Some varieties, such as amethyst, citrine, and tiger’s-eye, are valued as gem-
stones. Others are used in sandpaper and abrasives because of their resis-
tant, sharp-edged grains.

■ Analcime Crystals
The mineral analcime forms shiny, glass-clear crystals.They are usually
white, colorless, or gray, and may be tinted with green, yellow, or red.
Small but brilliant analcime crystals occur in the basalt that capsTable
Mountain in Golden, Colorado. It takes its name from the Greek an
(“not”) and alkimos (“strong”) in reference to its weak pyroelec-
tric properties. When heated, analcime’s surfaces develop weak
electrical charges.
Gift from Bethlehem Steel Corporation, through Gilbert L. Hole.

■ Polished Dolomite Marble Spheres
The reddish-pink dolomitic marble in these spheres was
originally dolomitic limestone. It has been metamorphosed
to marble and is intermixed with other metamorphic minerals,
including calcite, phlogopite mica, and serpentine. Dolomite is usu-
ally slightly harder than limestone and slightly more resistant to weather-
ing because it is less reactive to acid and has lower solubility. Dolomite is
named for Déodat de Dolomieu (1750–1801), a French mineralogist.
Gifts from Lafayette College, Easton, Pennsylvania, through Arthur Montgomery and Paul J. Roper, in recognition of Lafayette
alumnus Edwin B. Eckel’s contributions to the Society and to geology.

■ Beryl Crystal
White crystals like this specimen are relatively uncommon. Beryl crystals in
igneous pegmatites are often a meter or more (several feet) in length. A crys-
tal 8.5 m (27 ft) long and 2 m (6 ft) wide was quarried in Maine, and a 180
metric ton (200 ton) crystal was found in Brazil.
From the Bob Ingersol mine, Black Hills, Keystone, South Dakota. Gift from the Geology Museum, Colorado School of Mines,
Golden, Colorado.

■ Polished Variscite Spheres
Most variscite is pale green to bright emerald green. Intense blue colors
are fairly unusual. Variscite rarely forms distinct crystals; instead, it typically
fills small veinlets or forms nodules, crusts, or fine-grained masses. In these
spheres, the variscite is cut by veins of other minerals—crandallite (yellow,
tan, and white), wardite (blue-gray), and millisite (white). In North America,
variscite has been found only in the western United States. It is sometimes
used as a gemstone. The name variscite comes from Variscia, the region in
Germany where it was first identified.
Mined from Clay Canyon, Fairfield, Utah, by Edwin Over and Arthur Montgomery; shaped by B.F. Shepherd, Ingersoll-Rand Co.
The spheres are gifts from Lafayette College, Easton, Pennsylvania, through Arthur Montgomery and Paul J. Roper, in honor
of Lafayette alumnus Edwin B. Eckel.

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