Occurs in Pinal County.
Chemical Formula: Al2O3(SiO2)1.3-2.0·(nH2O)
Specific Gravity: 1.76-1.98
Hardness: 3.5
Allophane is a hydrous aluminum silicate mineral that forms as an amorphous, clay-like material. It is often found in soils and weathered rock formations.
Next Pinal County mineral: Alunite
Allophane is a mineraloid, which means it lacks a defined crystalline structure and is more amorphous in nature. It is often considered a type of clay mineraloid, though its exact classification can vary due to its non-crystalline characteristics. Allophane forms as a result of the weathering and alteration of volcanic glass, and it is commonly found in soils and weathered volcanic rocks.
The chemical composition of allophane can vary, but it generally consists of aluminum, silicon, and oxygen, along with some amounts of other elements. Its appearance can range from colorless to shades of white, yellow, brown, or green, depending on the impurities present in the mineraloid.
One of the distinctive properties of allophane is its ability to retain large amounts of water and other substances within its structure. This property makes it important in the context of soil science, as allophane-rich soils can have high water-holding capacities, influencing soil fertility and water availability for plants.
Allophane is often associated with volcanic environments and is formed through processes like the hydrothermal alteration of volcanic ash and glass. It can contribute to the overall mineralogical composition of volcanic soils and play a role in the cycling of nutrients and elements within ecosystems.