Page 37 - visitorGuide

of those ancient plants. This specimen was found above a coal layer in an
abandoned strip mine in Pennsylvania. It contains the remains of seed ferns
Neuropteris ovata and Alethopteris serlii.

■ Sphalerite
This slab, from the Commodore No. 5 mine in Creede, Colorado, shows hun-
dreds of near-perfect sphalerite crystals. Sphalerite is a heavy mineral that
often forms brilliantly shiny crystals but also occurs as dull, fine-grained
masses. This crystal slab formed one wall of a vein where ore minerals were
deposited from hot waters containing dissolved zinc, lead, and copper. This
specimen also contains small amounts of dark gray galena and brassy chal-
copyrite. Sphalerite gets its name from Greek sphaleros (“treacherous”) be-
cause its many colors and growth habits make it difficult to recognize and
because it is easily confused with other minerals such as galena and siderite.
Gift from the Geology Museum, Colorado School of Mines, Golden, Colorado.

■ Chalcocite, Azurite, and Malachite
This specimen (two pieces) is from the Kennecott Company’s Jumbo mine,
one of the largest chalcocite-rich ore bodies on record, near McCarthy, Alaska.
Chalcocite is the black mineral, azurite is the deep blue or deep violet mineral,
and malachite is the bright green one; all are important ores of copper. Chal-
cocite is named from the Greek chalkos (“copper”).
Gift from Edward M. MacKevett, Jr., U.S. Geological Survey, Menlo Park, California.

■ Sand Calcite Crystals
Sand calcite crystals like these occur in enormous quantities in a single bed
of sand near Badlands National Park.This specimen is from Rattlesnake Butte,
south of Interior, Washabaugh County, South Dakota.
Gift from the Department of Earth Sciences, University of South Dakota, Vermillion, through Valentine J. Ansfield.

■ Jadeite
Jadeite boulders of this size and character were common on the banks and in
the stream bed of Clear Creek, San Benito County, California, prior to the mid-
1950s. Because of the tremendous interest shown by amateur mineralogists
and rockhounds for jadeite and other lapidary materials, the course of Clear
Creek for several miles downstream and upstream from the Clear Creek mer-
cury mine was, within a few years following the discovery of jadeite, stripped
bare of all jadeite boulders.

Jadeite is one of two minerals that constitute jade, the gem material. Al-
though tons of jadeite have been picked up along the course of Clear Creek in
San Benito County, very little if any of it can be considered true gem-quality
jade. Jade is valued most highly when it is translucent or semi-transparent,
intensely and evenly colored, and without flaws. It gets its name from the
Spanish piedra de ijada (“stone of the side”) because it was applied to the
side of the body to treat kidney disorders.
Collected by Charles W. Chesterman and donated by him on behalf of the Department of Geology, California Academy of
Sciences, San Francisco.

■ Leaf Impression
When this finely laminated rock split, it revealed the dual impression of a
carbonized leaf. The leaf fell into shallow lake water where it was gradually
covered by layers of limy mud and silt that were later compressed and ce-
mented to form rock.
Purchased by the Society.

After you’ve finished viewing the specimens in these cases, you can take the stairs 27
back up to the first floor.

GARDEN LEVEL EXHIBITS