Page 58 - visitorGuide

■ Pyrrhotite Crystal with Sphalerite and Galena
This large, single golden-bronze crystal contains smaller crystals of dark
gray sphalerite and lead-gray galena. Pyrrhotite rarely forms large crystals
like this one. It is more often found in massive form, often associated with
nickel and copper minerals. Pyrrhotite’s metallic red-brown to golden-
bronze surfaces are often tarnished dark brown. Specimens, including
this one, collected in Santa Eulalia, Chihuahua, Mexico, are highly
iridescent. Most pyrrhotite is moderately magnetic.The strength
of magnetism in pyrrhotite is affected by how much iron is
“missing” from its atomic structure. Pyrrhotite is named from
the Greek pyrrhotes (“redness”).
Gift from Raymond M. Thompson, Englewood, Colorado.

■ Epidote
Epidote is a minor gemstone found in shades of green, tinted with
yellow, brown, or black. These two specimens represent two dif-
ferent kinds of epidote. The specimen with pistachio green granular
masses of epidote also contains black tourmaline and white quartz.The
specimen with dark green epidote crystals contains white calcite; it may
come from the Calumet iron mine in Chaffee County, Colorado, a location
known for short, well-formed epidote crystals like this one. Many epidote
crystals have lengthwise striations, or grooves. Transparent crystals are
strongly pleochroic, changing color from green to brown when the crystal is
viewed from different directions.

Epidote is formed in some igneous environments and is found in a va-
riety of metamorphic rocks. Its name is from the Greek epi (“over”) and
didonai (“to give”) because its crystals frequently grow larger on one side
than the other.

■ Modern Fan Coral
Coral is a general name for any of a large group of bottom-dwelling, attached,
marine coelenterates of the class Anthozoa.These two specimens of modern
coral are probably from the western Atlantic Ocean.

Modern Fan Coral

■ Quartz
This large quartz specimen represents one of many varieties of the rock
housed at GSA headquarters.

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