What is Pargasite?
Pargasite is a dark amphibole from calcic metamorphic rocks, valued for well-formed crystals and its role in tracing pressure, temperature and fluid conditions.
Mineralogy and crystal structure
Reference formula: NaCa2(Mg4Fe3+)(AlSi7O22)(OH)2. Pargasite is a monoclinic amphibole with variable iron, magnesium, aluminium and fluorine. Natural zoning is common, so the formula is an idealised reference. Pargasite is classified with silicates and has a monoclinic crystal system. Typical hardness is 5–6 on the Mohs scale and specific gravity is approximately 3.1–3.3.
Colour, lustre and habit
Typical colours include dark green, brown, black, green. The usual prismatic, acicular, granular habit and vitreous, pearly lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Pargasite forms in or is associated with marbles, skarns, amphibolites and metasomatic rocks rich in calcium and sodium. Important documented localities include Canada, Italy, Pakistan, Afghanistan, Norway, the United States and Japan.
Amphibole chemistry in a dark green crystal
Pargasite shows how a familiar amphibole architecture responds to calcium-rich metamorphic fluids and changing pressure-temperature conditions.
Collecting and care
Protect prismatic crystals from impact and avoid producing dust; retain matrix and locality information.
