Pargasite

Pargasite forms during contact metamorphism when granitic or syenitic magmas intrude impure dolomitic limestones. The heat and fluid interaction between silica-rich melts and carbonate-bearing country rock generates the calcium, sodium, magnesium, and aluminum proportions needed for amphibole crystallization. The Pargas district in Finland, the 1814 type locality, is the textbook example of this marble-granite contact aureole setting. The premier gem source at Kukh-i-Lal in Tajikistan's Pamir Mountains produces exceptional transparent crystals from a spinel-bearing marble skarn, where pargasite crystallizes alongside ruby-red spinel and yellow clinohumite from the same metamorphic event. Myanmar's Mogok valley hosts pargasite in ruby-bearing marbles formed under similar conditions. Crystals typically occur as stubby prismatic forms with the diagnostic 124 degree amphibole cleavage angles.

Pargasite shows vivid green to blue-green color in gem-quality material, driven by Fe²⁺ and Fe³⁺ substitution in the amphibole structure. Gem crystals from Tajikistan are typically 1-3 carat faceted stones with refractive index 1.61-1.63 and biaxial negative optic character. The diagnostic feature is amphibole cleavage at 124 and 56 degrees, visible on broken surfaces, which distinguishes pargasite from pyroxenes with their 90 degree cleavage. Specific gravity of 3.04-3.17 is moderate for the amphibole group. Hardness of 5-6 is softer than quartz. Crystals are prismatic and monoclinic, often with rhombic cross-sections. Streak is white to faintly greenish. Vitreous luster on crystal faces, pearly on cleavage surfaces.