Chalcopyrite
By Bob Farrar
by Bob Farrar
The Mineral of the Month for May is chalcopyrite. With its name meaning “copper pyrite”, chalcopyrite is a mineral of great economic importance as well as an interesting mineral for collectors.
Chalcopyrite consists of copper iron sulfide, CuFeS2. It crystallizes in the tetragonal system, with crystals usually appearing tetrahedral. Crystals are common, but massive material is more abundant. Chalcopyrite is typically brassy yellow, but often shows an iridescent tarnish. It is a dense mineral, with a specific gravity of 4.1 to 4.3. It is also rather brittle. Other physical properties include a hardness of 3.5 to 4.0, metallic luster, and poor cleavage. Chalcopyrite can be confused with pyrite, but chalcopyrite is usually more yellow, softer, and crystallizes in a different system. A test for copper is also diagnostic.
Chalcopyrite is the most important copper ore. While not as high in copper content on a percentage basis as some other minerals, chalcopyrite occurs in vast deposits. Among the most important formations economically are copper porphyries. A porphyry is an igneous formation in which crystals, or phenocrysts, began to grow before the groundmass solidified. Such deposits are often several kilometers in diameter. Well-known examples are found in Arizona, Mexico, and Chile. The small chalcopyrite grains typically found in porphyries are not of much interest to collectors, but upon weathering, they give rise to a myriad of colorful copper minerals, such as malachite and azurite.
Chalcopyrite occurs in a variety of environments in addition to porphyries. Among the more interesting are metallic ore veins, where it often occurs with other sulfides, such as sphalerite and galena. These formations, such as at the Joplin, MO district, often produce good crystal specimens. Ore veins may contain enough chalcopyrite to be economically important sources of copper, such as in Cornwall, England.
Chalcopyrite can also be formed by hydrothermal action in so-called “black smokers” on the sea floor, where spreading of the earth's crust is occurring. Such formations may be the source of copper that eventually formed the ores formerly mined in Copperhill, TN. New deposits continue to be formed in the oceans today.
Worldwide sources of chalcopyrite crystals are many. Famous European localities include Bulgaria, Romania, Germany, and England. Other worldwide localities include Russia, Japan, Australia, and Mexico. In recent years, particularly attractive crystals have been coming out of Morocco and China.
Chalcopyrite can be found in several localities in the Mid-Atlantic area. French Creek, in Chester County, PA, is particularly well known. It is found at Mineral Hill and other localities in Carroll County, MD, as well as in marble at the Marriotsville Quarry in Baltimore County. Chalcopyrite has also been reported from several of the traprock quarries in northern Virginia.
Chalcopyrite is thus both an important economic mineral and an interesting mineral for collectors. Attractive specimens are common enough that good pieces can be had for a reasonable price. It is therefore something that almost any collector can enjoy owning.
The Mineral of the Month for May is chalcopyrite. With its name meaning “copper pyrite”, chalcopyrite is a mineral of great economic importance as well as an interesting mineral for collectors.
Chalcopyrite consists of copper iron sulfide, CuFeS2. It crystallizes in the tetragonal system, with crystals usually appearing tetrahedral. Crystals are common, but massive material is more abundant. Chalcopyrite is typically brassy yellow, but often shows an iridescent tarnish. It is a dense mineral, with a specific gravity of 4.1 to 4.3. It is also rather brittle. Other physical properties include a hardness of 3.5 to 4.0, metallic luster, and poor cleavage. Chalcopyrite can be confused with pyrite, but chalcopyrite is usually more yellow, softer, and crystallizes in a different system. A test for copper is also diagnostic.
Chalcopyrite is the most important copper ore. While not as high in copper content on a percentage basis as some other minerals, chalcopyrite occurs in vast deposits. Among the most important formations economically are copper porphyries. A porphyry is an igneous formation in which crystals, or phenocrysts, began to grow before the groundmass solidified. Such deposits are often several kilometers in diameter. Well-known examples are found in Arizona, Mexico, and Chile. The small chalcopyrite grains typically found in porphyries are not of much interest to collectors, but upon weathering, they give rise to a myriad of colorful copper minerals, such as malachite and azurite.
Chalcopyrite occurs in a variety of environments in addition to porphyries. Among the more interesting are metallic ore veins, where it often occurs with other sulfides, such as sphalerite and galena. These formations, such as at the Joplin, MO district, often produce good crystal specimens. Ore veins may contain enough chalcopyrite to be economically important sources of copper, such as in Cornwall, England.
Chalcopyrite can also be formed by hydrothermal action in so-called “black smokers” on the sea floor, where spreading of the earth's crust is occurring. Such formations may be the source of copper that eventually formed the ores formerly mined in Copperhill, TN. New deposits continue to be formed in the oceans today.
Worldwide sources of chalcopyrite crystals are many. Famous European localities include Bulgaria, Romania, Germany, and England. Other worldwide localities include Russia, Japan, Australia, and Mexico. In recent years, particularly attractive crystals have been coming out of Morocco and China.
Chalcopyrite can be found in several localities in the Mid-Atlantic area. French Creek, in Chester County, PA, is particularly well known. It is found at Mineral Hill and other localities in Carroll County, MD, as well as in marble at the Marriotsville Quarry in Baltimore County. Chalcopyrite has also been reported from several of the traprock quarries in northern Virginia.
Chalcopyrite is thus both an important economic mineral and an interesting mineral for collectors. Attractive specimens are common enough that good pieces can be had for a reasonable price. It is therefore something that almost any collector can enjoy owning.
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