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Occurs in Pinal County.

Alunite. Al Copley photo.

Chemical Formula: KAl3(SO4)2(OH)6

Specific Gravity: 2.6-2.9

Luster: Vitreous to pearly

Hardness: 3.5-4

Alunite is a sulfate mineral that is often found in the oxidized zones of sulfide ore deposits. It typically appears as white to pale colors and can sometimes be used as a source of aluminum.

Next Pinal County mineral: Amesite

MinDate Alunite

Alunite is typically found in hydrothermal alteration zones associated with volcanic activity. It is a sulfate mineral and is composed of potassium, aluminum, sulfur, and oxygen.

Alunite is recognized for its characteristic white to pale colors, including shades of gray, yellow, and reddish-brown. It often occurs in the form of crystalline masses or fine-grained aggregates. One of the distinctive features of alunite is its association with certain ore deposits, particularly those that contain valuable metals like gold and silver.

The mineral forms in environments where acidic fluids rich in sulfur and potassium interact with rocks containing aluminum-rich minerals. Alunite is commonly found in volcanic rocks, such as rhyolites and andesites, and it often forms in the presence of hot springs and geothermal activity.

Alunite has historical significance due to its use in the past for the production of alum, a compound with applications in dyeing and tanning. The name “alunite” is derived from “alum,” highlighting this historical association. However, the use of alunite for alum production has diminished over time due to the availability of more cost-effective methods.

Geologically, the presence of alunite can serve as an indicator of hydrothermal alteration and the potential for associated mineral deposits. In mineral exploration, the presence of alunite can be a clue that valuable metals like gold and silver might be found nearby.