Tour Three Mines

Sterling Hill Mine
Deep in the hills of New Jersey lie two of the world's most unusual mines: Sterling Hill and nearby Franklin. A greater variety of minerals has been found here than at any other deposit, and 35 of Sterling's minerals aren't found anywhere else. The mines were a major source of zinc from the 1880s until they closed—Franklin mine in 1954, Sterling Hill mine in 1986.

Minerals That Glow in the Dark. When certain materials are exposed to invisible ultraviolet light, they give off visible light. Franklin-Sterling Hill, New Jersey, is the fluorescent mineral capital of the world. Over 70 kinds of minerals from this location fluoresce, creating a riot of color under ultraviolet light.

Copper Queen Mine
In less than a century, from 1881 to 1975, approximately 3.6 billion kg (8 billion lb) of copper were removed from the Bisbee area. That is enough to form a cube of copper with each side the length of a football field! The Bisbee area also yielded silver, gold, lead, and zinc.

Minerals From Bisbee. The Bisbee mining locality is famous worldwide for the diversity and magnificence of its minerals, which are favorites of collectors. Bisbee has produced over 200 kinds of minerals—most notably azurite, malachite, and other copper minerals.

When Copper Was Queen. Bisbee's history is laced with action, danger, and plenty of hardship. In 1877, copper was discovered in an uninhabited canyon in the Mule Mountains of southeastern Arizona. In just a few decades Bisbee grew from a prospector's camp to…a lively boom town. In 1905, it was Arizona's largest city. The reason for this meteoric growth was simple… the age of electricity had dawned. Here, copper wires light up turn of the century New York City. Meanwhile, back at Bisbee… miners worked by candlelight. Each miner was issued three candles per 10 hour shift. Once the copper ore had been drilled and blasted from hard rock… mules hauled it to hoists, which lifted the ore to the surface. In the early 1900s, about a hundred mules were kept in Bisbee's underground tunnels.

Morefield Mine
Many people picture mine tunnels in drab shades of brown and gray. But at Morefield mine, vivid bands of blue green amazonite—a variety of feldspar—glisten like a tropical sea. The mine cuts into a pegmatite, a type of deposit characterized by large crystals of feldspar and quartz with a great variety of other minerals. Morefield is mined for amazonite, used as an ornamental stone. Amazonite is found only in pegmatites. Like many pegmatite deposits, the Morefield's is small--only about 300 m (985 ft) long and 60 m (197 ft) deep. In the early 1900s, Silas V. Morefield first worked this deposit from the surface for amazonite and mica.

Amazonite. Amazonite, Morefield's major ore, is used in jewelry and as an ornamental stone. Morefield is one of the few locations in the United States where amazonite is mined.

How Did This Deposit Form? Around 250 million years ago, molten rock (magma) pushed toward the surface of the Earth and began to cool. The last of the magma to cool was rich in water and rare elements. It penetrated fractures in the surrounding rock, then slowly cooled from the outer edges inward, forming the gigantic crystals of the pegmatite.