Cornwallite with Barite on Enargite (#86)

Micro crystals of lustrous dark green cornwallite in a vug of massive enargite.
North America Tintic District, Juab County, Utah 3" x 2" x 1 ¼"


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Cornwallite, Cu5(AsO4)2(OH)4, is another uncommon secondary copper arsenate found in the oxidized zones of copper ore deposits (compare with specimen #85), and first discovered in Cornwall, England. Enargite, Cu3AsS4, is a primary copper ore. For barite, see Specimen #28. The word ''vug" in the label, means a small or medium-sized cavity in a rock.

Several of the minerals in this display came from the Tintic District in Juab County, Utah. A mining district is simply an area in which mining - generally a significant amount of mining - has or does occur. The Tintic District was an active mining district in the second half of the 19th century and into the 20th century. Production declined during the second half of the 20th century, and the last mine closed in 2006. Only sporadic activity occurs there now.

The Tintic District produced silver, gold, lead, copper, and zinc, in that order. At current prices, the 20 million tons of metal produced would be worth $3-4 billion.

The most prominent member of the Church of Jesus Christ of Latter-day Saints to be involved in mining in the Tintic District was Jesse Knight. His generous support of Brigham Young University during very difficult times for the school was made possible by his mining enterprises (and, of course, a generous heart). The Jesse Knight Building (JKB) is named in his honor.