Gla

Gla nw walls

Gla se gate

Plan of the Palace of Gla

Amth20

Gla - Modell of archaeological site

Glaucophane is a mineral belonging to the amphibole group, characterized by its blue to lavender color, which is attributed to the presence of iron and sodium in its chemical composition. Its name is derived from the Greek words glaukos, meaning blue, and phainesthai, meaning to appear, referring to its distinctive coloration. Glaucophane forms under high-pressure, low-temperature conditions typical of subduction zones, making it a key mineral in the study of metamorphic rocks, particularly those known as blueschist facies.

Properties and Composition

Glaucophane has the chemical formula Na₂Mg₃Al₂Si₈O₂₂(OH)₂. It is a sodium magnesium aluminum silicate mineral. The presence of sodium (Na) and magnesium (Mg) in its structure is crucial for its formation under specific geologic conditions. Glaucophane is recognized by its monoclinic crystal system and prismatic crystal habit, often forming elongated, needle-like crystals. Its hardness on the Mohs scale is typically between 6 and 6.5, making it relatively hard among silicate minerals.

Formation and Occurrence

Glaucophane is primarily found in metamorphic rocks that have undergone high-pressure, low-temperature conditions, such as those found in subduction zones where oceanic crust is forced into the mantle. These conditions lead to the formation of blueschist facies, where glaucophane is often a major component. The mineral is commonly associated with other high-pressure minerals such as lawsonite, jadeite, and garnet. Glaucophane-bearing rocks are significant in geology as they provide insights into the tectonic processes occurring at convergent plate boundaries and the conditions deep within subduction zones.

Geological Significance

The presence of glaucophane and associated minerals in metamorphic rocks is indicative of specific pressure-temperature conditions and can be used to trace the geodynamic history of orogenic belts and subduction zones. The study of glaucophane-containing rocks contributes to our understanding of plate tectonics, particularly the processes of subduction, uplift, and exhumation of terranes. Glaucophane's stability at high pressures but relatively low temperatures makes it a key index mineral for identifying and studying blueschist facies metamorphism.

Uses and Applications

While glaucophane is not widely used in commercial applications due to its rarity and the difficulty of extracting it from its host rocks, it is of significant interest in academic and research settings. Geologists study glaucophane and its associated rocks to gain insights into the conditions of the Earth's crust and mantle at convergent plate boundaries. In addition, its distinctive blue color can make it an attractive specimen for mineral collectors.

See Also

• Amphibole
• Metamorphic Rocks
• Subduction Zone
• Plate Tectonics
• Blueschist