Definition Vesuvianite, also known as idocrase, is a calcium aluminum silicate mineral with the chemical formula Ca₁₀(Mg,Fe)₂Al₄(SiO₄)₅(Si₂O₇)₂(OH,F)₄. It commonly occurs in metamorphic rocks formed under high-temperature conditions, particularly in contact metamorphosed limestones and skarns.
Overview Vesuvianite is typically found in metamorphic environments where igneous intrusions interact with carbonate-rich rocks, leading to the formation of skarn deposits. It is an indicator mineral in such geological settings and can provide insight into temperature and pressure conditions during metamorphism. Due to its variable composition, vesuvianite can incorporate a range of elements, including magnesium, iron, manganese, and boron. The mineral is also known for forming well-developed crystals, often tetragonal in habit, and is sometimes used as a gemstone when transparent and suitably colored.
Etymology/Origin The mineral was first described in 1795 from samples collected on Mount Vesuvius in Italy, from which it derives its name. The alternative name "idocrase" comes from the Greek words idos (form) and krasis (mixture), referring to its crystal form, which resembles that of other minerals, suggesting a blended or composite appearance.
Characteristics Vesuvianite typically crystallizes in the tetragonal crystal system. It has a Mohs hardness of approximately 6.5 and exhibits a vitreous to resinous luster. Its color ranges widely, including green, brown, yellow, blue, purple, and colorless, with green being the most common. The mineral has a white streak and may display weak pleochroism. It is generally translucent to transparent and occurs in prismatic crystals, often with square or octagonal cross-sections. Vesuvianite is distinguishable by its specific gravity (3.3–3.4) and refractive index (typically 1.70–1.72).
Related Topics
- Skarn: A type of metamorphic rock where vesuvianite commonly forms.
- Metamorphic petrology: The study of rocks transformed by heat and pressure, relevant to vesuvianite formation.
- Gemology: Vesuvianite is occasionally cut into gemstones, particularly in rare blue or purple varieties.
- Mount Vesuvius: The type locality where the mineral was first identified.
- Calcium aluminum silicate minerals: A broader group including garnet, epidote, and other silicates that share geochemical affinities.