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MINERALOGICAL MUSEUM

Rhodochrosite, Sweet Home Mine, Alma, Colorado

Colorado Rhodochrosites
From the Collection of Dave Bunk

February 6 – May 12, 2013

Among the hundreds of gold and silver mines that operated in Colorado from the 1870’s to the present are many that also produced vivid red-pink rhodochrosite specimens. Although the Sweet Home Mine in Park County, Colorado is best known for the rhodochrosite specimens mined during the 1990’s, many other Colorado mines have produced aesthetic examples of this manganese carbonate mineral.

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Although the Mineralogical Museum was founded with the gift of the collection of Irenee du Pont, Sr., it has grown to encompass specimens gifted or made possible by many generous donors, including Mrs. David Craven, Alvin B. Stiles and Frederick Keidel. Because of our intimate space, we have chosen to focus on individual displays that illustrate particular mineralogical concepts or themes. These include gem minerals from the du Pont collection mined in the early 20th century, as well as more recent finds of minerals from North America. Newly installed display cabinets with fiber optic lighting provide accurate color balance for specimens from the wire silvers to the vivid orange wulfenites.

The new exhibition of minerals from Delaware, Maryland and Pennsylvania includes both specimens from mines that have not operated in decades and others discovered more recently, such as the calcite from the Roosevelt Quarry, York, Pennsylvania, mined in 2005.  The diversity of the geological environments is reflected in the diversity of the minerals themselves: blue celestines from operating limestone quarries; green pyromorphite from long abandoned lead mines; pyrite from nearby iron mines.

Pyromorphite: Calbeck Fells, Cumbria, England (6 cm x 4 cm x 4 cm)

The minerals exhibited here are from the collection of Irenee du Pont, Sr. (1876 – 1963), whose collection was gifted to the University of Delaware in 1964. Du Pont purchased much of his collection from George Kunz, Vice-President of Tiffany & Co., in 1919. This display emphasizes minerals from extinct localities – deposits that have been mined out or even mines that have vanished into later open pit mining operations.

Two boxes of tourmaline crystals are part of a set of four fitted boxes with specimens from the Himalaya Mine, San Diego County, California, acquired from Kunz. The Himalaya Mine opened in 1898 and was the world’s largest producer of tourmalines, largely exported to China for carving as snuff bottles and other small objects.

The lead and bismuth specimens in this display are important rarities, as these elements are almost always found in combination with other elements in minerals and not in their native states.

Rhodochrosite: Santa Isabella Vein, Huallapon Mine, Pasto Bueno, Peru (9 cm x 6 cm x 3.75 cm)

All minerals are crystalline, with orderly and repeating arrangements of atoms. Growth occurs by the addition of atoms to the arrangement. If growth takes place in an open space or in soft material, a crystal, reflecting the internal atomic arrangement may form. Although ideal crystals are perfect shapes, many actual crystals are distorted due to variations in growth over time.

Although, there are enormous variations in crystal shapes, they can all be grouped into six crystal systems based on the geometry of the internal structure.

Calcite on sphalerite: Elmwood, Tennessee (21.5 cm x 17.5 cm x 13 cm)

These minerals illustrate the breadth of specimens found in the United States and Canada. Most of the minerals on display were the by-product of mining operations for copper, lead, zinc and other metals. The term “lunch box” specimen can be applied to some, as miners often removed fine crystal specimens during work hours, sparing them from the ore crushers. There have been few ventures strictly for the mining of mineral specimens.

Goethite: Rio Tinto District, Andalusia, Spain (18 cm x 16 cm x 14 cm)

Almost all caves are limestone, with light- colored white to beige stalactites and stalagmites. Other unique cave deposits include vivid pink rhodochrosite stalactities in Argentina, deep green banded malachite formations in Republic of Congo and exotic specimens such as this goethite from Spain.

Hematite pseudomorph after magnetite: Altiplano de Payun Matru, Argentina (3.5 cm x 3.5 cm x 12.5 cm)

A pseudomorph is a “false form” – one mineral adopting the shape of another; the second mineral is said to be a pseudomorph after the first. Pseudomorphs may be formed in different ways;

- A mineral formed under certain conditions may change to another, chemically similar mineral with a different atomic arrangement, if the conditions change. The illustrated hematite is an example of this type
- A mineral may be replaced by another that has such a great chemical difference that it is considered a replacement pseudomorph
- A mineral may coat another, preserving the original shape and forming an encrustation pseudomorph. All of these are illustrated by specimens on exhibition.

Crystals may also deviate from their ideal shapes because of internal defects in atomic arrangement or because of the manner in which the atoms have been bonded to the surfaces of crystal faces during growth. Elongated or twisted crystals sometimes result from these arrangements.

• University of Delaware   •   Newark, DE 19716   •   USA
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