Natural crystal microcline is a common, but not well-known mineral. It has been used as a semiprecious stone, as the varieties amazonite and perthite. Microline is coming from the class of framework silicates. Natural crystal microcline has triclinic crystal system and composed from potassium aluminum silicate. Amazonite is a deep green variety, while perthite is veined (almost zebra-striped), the result of lamellar intergrowths found inside the crystal. Colors are available in green, white, pink, gray, red, yellow, colorless, and blue-green.
The name natural crystal microcline comes from the Greek words mikros, meaning “small,” and klinein, meaning “to incline,” because the cleavage planes lean very slightly away from 90 degrees. Amazonite is named after the Amazon River, but although amazonite is widely found in Brazil, it is not known to be found near the Amazon.
Well-shaped crystals and twins, and crystals of green amazonite, are sought after. Microline has refractive index in 1.522-1.530 range and specific gravity is between 2.56-2.58. Amazonite is usually polished as a cabochon. Natural crystal microcline can be faceted in rare cases (for collectors). It is otherwise cut as beads, cabochons, and cameos, or carved as objects. The perfect of natural crystal microcline is perfect in one direction and good in another. Its habit is prismatic crystals and massive, often with exsolved white albite.
Natural crystal microcline is a polymorph of orthoclase and sanidine, minerals that share the same chemistry but have different crystal structures. Natural crystal microcline is formed in igneous rocks that cooled slowly. It has vitreous luster and its fracture is uneven. It is found in granites, granite pegmatites, hydrothermal veins, and schists and gneisses, and as grains in many sedimentary rocks. Natural crystal microcline has a 0.008 birefringence and a 0.012 dispersion. The hardness finished at level 6-6.5.
Natural crystal microcline as a unique natural gemstone also occurs in compact crystal aggregates. In some areas, fine amazonite clusters are mixed with smoky quartz crystals, producing beautiful specimens. Amazonite gets its green color from small impurities of lead. Natural crystal microcline is found in the USA, Brazil, Zimbabwe, Russia, Australia, Namibia, Madagascar, India, Canada, and Tanzania. The deep green is a strong indicator natural crystal microcline. Striated crystals are common.
