Page 49 - visitorGuide

several ways: by gradual cooling of the magma itself, by chemical reactions
between the magma and pieces of fallen rock, and by crystallization of material
that melted when it fell into the magma.
Gift from the Department of Geology, California State University, San Diego, through Richard L. Threet.

■ Rock Crystal Quartz
Rock crystal is transparent, colorless quartz.This rock crystal specimen weighs
86.6 kg (191 lbs). Rock crystal boulders ten times larger have been found in
Calaveras County, California, and crystals weighing 4 metric tons (almost
9000 lbs) have been found in Brazil. Rock crystal is used for lenses, wedges,
and prisms in optical instruments and for frequency control in electronics.
It can be grown synthetically in laboratories to ensure that it has the exact
electrical and optical properties needed for industrial use. As a gemstone, it is
fashioned into beads or other ornamental objects.
Courtesy of the National Institute of Standards and Technology, Time and Frequency Division, through Ralph F. Desch.

■ Fossil Fish
Before stepping in to view the Council Room specimens, notice the Fossil Fish
between the two sets of double doors. These fossilized armored herring are
Diploymystus dentatus, members of a marine species that adapted to living in
freshwater. They have living relatives in the coastal waters off Peru and east-
ern Australia. This specimen is from the Green River Formation of the Fossil
Syncline Basin some 19 km (12 miles) west of Kemmerer, Wyoming.

When these two fish died, they sank to the bottom of an ancient lake. Grad-
ually, they were covered by a thick sequence of thin-layered sediments and
organic material.The fleshy parts of the fish probably were destroyed shortly
after they died, but their fins, scales, and bones were preserved as the sedi-
ments compacted and cemented to form rock. Millions of years later, these
rock layers were exposed at Earth’s surface. Museum workers carefully re-
moved the rock outer layer, leaving the bones in relief. Although the precise
age of the fish deposit is not known, it is probably late early Eocene, possibly
55 million years old.
Gift from the Department of Geology, University of Wyoming, Laramie, through Paul O. McGrew.

The Council Room was constructed to accommodate the Society’s Council, which
meets at least twice a year to discuss management of GSA’s affairs. In addition to
the geological specimens listed, the room also houses books from the collection of
Richard A.F. Penrose, Jr. On display are gifts from geological organizations all over the
world, including Iran and China.

■ Photo of Richard A.F. Penrose, Jr.
As you enter the Council Room through the right-hand set of double doors,
you will first see a photo of the Society’s benefactor, Richard A.F. Penrose, Jr.,
displayed in the bookcase on your right. If you haven’t already visited the Pen-
rose Room and Library on the first floor and would like to learn more about
him, turn to p. 16.

■ Quartz Crystals
Small quartz crystals formed along two crystal faces of the larger quartz crys-
tal. Crystal size is affected by the temperature, pressure, and chemistry of the
fluids from which the crystals grow.

39SECOND FLOOR EXHIBITS