Microcline: Gemstone Information
It is the common potassium feldspar in pegmatites where it takes the place of orthoclase. It can form the largest known crystals of any mineral (in a pegmatite in Kareliya, Russia, a microcline mass weighing over 2000 tons showed the form of a single crystal!). Microcline is also common in metamorphic rocks in gneisses and in sedimentary rocks in arkoses and conglomerates.
Notable deposits are found in Italy, Norway, Madagascar, Namibia, Zimbabwe, India, Russia, Brazil, Australia, Canada and the USA. Amazonite localities include USA (Colorado, California, Montana, Pennsylvania, Virgina–Amelia County, deep, blue-green, translucent), Canada (Ontario–Renfrew and Parry Sound districts and Quebec–
Kipawa), Brazil, India (Kashmir district and elsewhere), Kenya, Tanzania, Madagascar (Anjanabonoina, Andina, Immody and Mahabe), Namibia and South Africa. Russia the biggest gem amazonite deposits in the world are located in an area 1 km2 at Ploskaya Gora and Parus mountain, 80 km east from Lovozero, Kola Peninsula
(there are more then ten pegmatite veins from 10 to 300-m long and from 0.5 to 30 m thick), also in Russia relatively large quantities of amazonite used as gemrock has come from pegmatite masses near Miass in the Ilmen range of the southern Ural mountains, Afghanistan at Madan Shar, Kabul Province in small deep blue-green, semi-translucent crystals and Australia (Broken Hill, New South Wales – also in semitranslucent masses). Green microcline is reported from various localities in Brazil.
Opaque to translucent, rarely transparent. Simple and polysynthetic twinning are ubiquitous and perthitic intergrowth with albite, extremely common. Reflections from incipient cleavages give polished surfaces a
• Lustre: Vitreous
• Colour: Commonly white to pale yellow or salmon, also may be blue to green in the microcline variety amazonite. It should be noted that although nearly all green potassium feldspar is microcline, much microcline, as well as most orthoclase, is commonly white, flesh- or salmon-pink.