Pargasite — A Collector's Amphibole
Pargasite — A Collector's Amphibole
Sodium-calcium amphibole occasionally cut as a faceted gem
Pargasite is a sodium-calcium amphibole mineral with the simplified composition NaCa2(Mg,Fe)4Al(Si6Al2)O22(OH)2, occasionally encountered in the cutting trade as a collector's faceted gemstone or, more often, as a translucent cabochon. Pargasite is a member of the amphibole supergroup, closely related to hornblende, and named after Pargas in southwestern Finland, the type locality from which the species was first described in 1814. Most pargasite is opaque or translucent and unsuitable for cutting; transparent crystals adequate for faceting are rare and the species is firmly in the collector category rather than the commercial trade.
Mineralogy
Pargasite forms in metamorphic rocks, particularly in marbles and amphibolites, where the bulk chemistry permits sodium and calcium amphibole crystallisation. Crystals are prismatic, often elongated along the c-axis, and may reach several centimetres in length. The mineral is monoclinic with a hardness of 5 to 6 on the Mohs scale, a specific gravity around 3.0 to 3.2, and refractive indices in the range 1.61 to 1.65. Cleavage is good in two directions at characteristic amphibole angles of approximately 56 and 124 degrees, a structural feature shared across the amphibole supergroup.
Colour ranges from green through brown to dark grey-green, with the green saturation depending on iron and chromium content. Vivid green chrome-bearing pargasite has been reported from a few localities and is the most prized variety from a gem perspective.
Sources
Notable pargasite localities include Pargas in Finland (the type locality), Mogok in Myanmar, the Hunza valley in Pakistan, several occurrences in Tanzania including parts of the Merelani region, and various marble-hosted localities in Russia. Mogok material, in particular, has produced occasional faceted stones in the green-to-brown range. Sizes are typically small; faceted pargasite above two carats is unusual.
In the trade
Pargasite appears occasionally in collector and rare-stone catalogues but is not a meaningful commercial gem material. For Skyjems clients with collector interest in unusual species, pargasite is one of several amphibole-supergroup gems alongside actinolite, tremolite, and hornblende that occasionally yield faceted stones. Identification requires gemmological testing — refractive index, specific gravity, and spectroscopy — to distinguish pargasite from related species.