Pargasite
Chemical formula: NaCa₂(Mg₄Al)(Si₆Al₂)O₂₂(OH)₂
Pargasite is a mineral from the amphibole group, characterized by variable color from light brown to dark green, occurring in metamorphic and igneous rocks.
Description
## Characteristics Pargasite is a mineral belonging to the amphibole group, which are chain silicates. It typically occurs as well-formed, prismatic or tabular crystals, often with a rhombic cross-section. Aggregates can be granular or massive. The color of pargasite is variable and includes shades from light brown, through brown, brownish-green, to dark green and black. This mineral has a vitreous luster. ## Physical Properties The hardness of pargasite on the Mohs scale is 5-6. It has perfect cleavage along {110} planes. The luster is vitreous. The streak of pargasite is light grayish-green to brownish-green. The fracture is uneven to conchoidal. ## Colors and Varieties Pargasite occurs in a wide range of colors, from light brown and brown, through brownish-green, to dark green and black. Color variations are often associated with the presence of various trace elements in its crystal structure. ## History and Name Pargasite was described in 1814. The mineral's name comes from the locality Pargas (now Parainen) in Finland, where it was first discovered and identified. ## Uses Pargasite has no significant industrial applications. It is a mineral of interest mainly to collectors and researchers due to its occurrence in specific geological environments and its color and crystallographic variability.
Diagnostic features
## Identification Pargasite can be identified by its characteristic prismatic or tabular habit, vitreous luster, and variable color from brown to dark green. A key diagnostic feature is its perfect cleavage in two directions, forming angles characteristic of amphiboles. A hardness of 5-6 on the Mohs scale also aids in identification. ## Distinguishing from Similar Minerals Pargasite is sometimes confused with other amphiboles, such as hornblende. Differences are often subtle and require chemical or optical analysis. It is distinguished from pyroxenes by its cleavage angle (amphiboles have angles of approximately 56° and 124°, pyroxenes approximately 87° and 93°). ## Crystal Forms Typical crystal forms of pargasite are prisms and tablets. Crystals are often well-formed, with a rhombic cross-section. It also occurs as granular, massive, or fibrous aggregates.
Geological environment
## Genesis Pargasite forms mainly in metamorphic rocks, especially in marbles and skarns, where it is a product of contact or regional metamorphism of carbonate sedimentary rocks with an admixture of magnesium and aluminum. It can also occur in some igneous rocks, such as syenites and diorites, and in pegmatites. ## Mineral Associations Pargasite often co-occurs with minerals such as calcite, dolomite, diopside, garnets (e.g., grossular), vesuvianite, phlogopite, spinel, quartz, and plagioclase. ## Localities Known occurrences of pargasite include Pargas (Parainen) in Finland, where it was first discovered. Other important localities include Tvedalen in Norway, the Franklin area in New Jersey (USA), as well as areas in Canada, Russia, Myanmar, and Madagascar.
Rarity
Common
Collector aspects
## Quality Criteria The most valued pargasite specimens are those with well-formed, large, and distinct crystals, characterized by intense and uniform color, especially dark green or brown. Transparency and the absence of visible inclusions also increase collector value. Specimens with aesthetic mineral associations are also highly prized. ## Market Prices Market prices for pargasite vary and depend on the size, quality, color, and rarity of the specimen. Small, poorly formed crystals may be available for a few tens of zlotys, while large, well-formed, and aesthetic specimens, especially those with rare colors or interesting associations, can fetch prices from several hundred to even several thousand zlotys. ## Popular Localities Particularly prized specimens come from localities such as Pargas in Finland, Tvedalen in Norway, and some locations in the USA and Canada, where crystals of exceptional quality and size are found.
Care and storage
## Cleaning Pargasite specimens can be cleaned using a soft brush and lukewarm water. For more stubborn dirt, a mild soap can be used, followed by thorough rinsing with clean water. It is important to dry the mineral thoroughly after washing to prevent scale buildup or water stains. ## What to Avoid Avoid using strong acids and bases, which can damage the mineral's surface. Pargasite is sensitive to rapid temperature changes, so it should not be exposed to extreme heat or cold. Prolonged exposure to direct sunlight may, in some cases, lead to slight changes in color hue, although this is not a common phenomenon for this mineral. ## Storage Pargasite is best stored in a dry place, away from dust and direct sunlight. For storing individual specimens, soft pouches or padded boxes can be used to prevent scratches. Larger specimens can be displayed on open shelves, provided they are regularly dusted.