Page 42 - visitorGuide
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■ Blue Celestite Crystals
These clear blue, gem-quality crystals of celestite are from Katsepe-Majunga,
Madagascar. Celestite is named from the Latin caelestis (“of the sky”) and was
recognized in 1820 when it was found during excavation of the Erie Canal in
Niagara County, NewYork. Crystals up to 45 cm (1.5 ft) long have been found in
dolomite caves along Put-in-Bay on South Bass Island near the southern shore
of Lake Erie in Ohio.
Gift from Raymond M. Thompson, Englewood, Colorado.
■ Rhombohedron Calcite
This large honey-colored specimen, from near Big Bend National Park,Texas,
illustrates how calcite forms rhombohedrons. Calcite is doubly refractive,
bending light rays along double paths. Looking at print through a clear calcite
rhombohedron produces a double image.
Gift from Harrison Cobb, Boulder, Colorado.
■ Indicolite Tourmaline Indicolite Tourmaline
This is a single crystal of indicolite, the dark
blue variety of tourmaline.This crystal’s
flat base is unusually large and defined.
The lengthwise striations and the crystal’s
convex, rounded triangular cross section
are typical of tourmaline.
Gift from Raymond M. Thompson, Englewood, Colorado.
■ Fluorite and Calcite
Underneath the “fuzzy” surface of this speci-
men are large, box-shaped transparent crys-
tals of yellow and purplish fluorite. The “fuzz”
is actually a thin layer of tiny, sharp calcite crys-
tals that grew over the larger fluorite crystals.This
specimen is from Cave-in-Rock, Hardin County, Illi-
nois. Fluorite is commonly blue or purple, but occurs in many other colors. It
is the ore of fluorine, and is used in glass and enamel and in the manufacture
of hydrofluoric acid.
Gift from John W. Palmer, Cave-in-Rock, Illinois.
As you make your way down the first-floor hallway, you will come to a rock sculpture
in the west atrium. At 1.7 billion years old, this migmatite specimen is even older than
the Silver Plume granite (“Big Al”) in the main lobby. (See framed poem mounted on wall
southeast of rock.)
■ Migmatite
Found in Rocky Mountain National Park on the west side of the Bierstadt mo-
raine, along the road to Bear Lake, is part of the Precambrian Idaho Springs
Formation, a thick sequence of sedimentary and igneous rocks that were
formed 1.7 billion years ago. In the last portion of its history, this piece of rock
was broken away from the layers of Idaho Springs Formation and deposited in
the flank of a glacial moraine. Its surface has been smothered by gravel, sand,
and silt carried by streams, glaciers, and wind.This ancient rock is displayed at
GSA headquarters through a special agreement with the National Park Service.
Indefinite loan, courtesy of J.L. Dunning, Superintendent, Rocky Mountain National Park; National Park Service Association
No. 662, Catalog No. 6201. Selected by R. Dana Russell of Estes Park, Colorado, author of the accompanying poem-history.
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