Labradorite

The geological type area for labradorite is Paul's Island near the town of Nain in Labrador, Canada. It has also been reported in Poland, Norway, Finland and various other locations worldwide, with notable distribution in Madagascar, China, Australia, Slovakia and the United States. It also is found in metamorphic amphibolites and as a detrital component of some sediments. Common mineral associates in igneous rocks include olivine, pyroxenes, amphiboles and magnetite. ==Labradorescence==

Labradorite can display an iridescent optical effect (or schiller) known as labradorescence. The term labradorescence was coined by , who defined it (labradorization) as follows: The cause of this optical phenomenon is phase exsolution lamellar structure, The effect is visible when the lamellar separation is between ; the lamellae are not necessarily parallel; The lamellar separation only occurs in plagioclases of a certain composition; those of calcic labradorite (50–70% anorthite) and bytownite (formula: , i.e., with an anorthite content of ~70 to 90%) particularly exemplify this. Another requirement for the lamellar separation is a very slow cooling of the rock containing the plagioclase. Slow cooling is required to allow the Ca, Na, Si, and Al ions to diffuse through the plagioclase and produce the lamellar separation. Therefore, not all labradorites exhibit labradorescence (they might not have the correct composition, cooled too quickly, or both), and not all plagioclases that exhibit labradorescence are labradorites (they may be bytownite). ==Spectrolite==

Spectrolite is an uncommon variety of labradorite exhibiting a high degree of labradorescence. It exhibits a richer range of colors than other labradorites as for instance in Canada or Madagascar (which show mostly tones of blue-grey-green). Due to the unique colors mined in Finland, spectrolite has become a brand name for material mined only there. Sometimes spectrolite is incorrectly used to describe labradorite whenever a richer display of colors is present, regardless of locality: for example, labradorite with the spectrolite play of colors has sometimes described material from Madagascar. Finnish geologist Aarne Laitakari (1890–1975) described spectrolite and sought its origin for years when his son Pekka discovered a deposit at Ylämaa in south-eastern Finland, while building the Salpa Line fortifications there in 1940. The quarrying of spectrolite began after the Second World War and became a significant local industry. In 1973, the first workshop in Ylämaa began cutting and polishing spectrolite for jewels. After that, a gem center was established in Ylämaa with training for gem-cutting accompanied by an annual Gem and Mineral Show initiated by Esko Hämäläinen, mayor of Ylämaa municipality. ==Gallery==

File:Labradoryt, Madagaskar.JPG|Polished block from Madagascar File:Labradorite detail.jpg|Detail of labradorite File:LabradoriteAMD.jpg|Polished labradorite 18 × 20 cm File:Labradorite (UCL Geology Collections).jpg|Polished labradorite from UCL Geology collections File:Labradorite with rare colours.JPG|Labradorite with rare colors (spectrolite) File:Ladrador iridescence.jpg|Polished labradorite File:Grey labradorite.jpg|Iridescence effect on grey labradorite File:Labradorescence.jpg|Labradorescence in labradorite File:LabradoriteOslo.jpg|Spectrolite from Ylämaa, Finland File:Labrador spektrolit - Ylamaa, Finlandia.jpg|Spectrolite – Ylämaa, Finland. File:Labradorescence in labradorite.webm|upright|Video of labradorescence in labradorite, visible as the angle of view changes File:Spectrolite1.jpg|Polished spectrolite showing the color play ==See also==