The Dynamic Earth @ National Museum of Natural History

Main Menu > Rocks and Mining > Tour Three Mines > 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.

[Illustration: Morefield mine shafts and tunnels showing amazonite veins.]

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. Today, the Morefield is mined for amazonite.

		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.