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Aventurine feldspar or sunstone can be confused with orange and red aventurine quartzite, although the former is generally of a higher transparency. Aventurine is often banded and an overabundance of fuchsite may render it opaque, in which case it may be mistaken for malachite at first glance.
Sunstone is a microcline or oligoclase feldspar, which when viewed from certain directions exhibits a spangled appearance. It has been found in Southern Norway , Sweden , various United States localities and on some beaches along the midcoast of South Australia.
The words aventurine and aventurescence derive from the Italian "a ventura", meaning "by chance". This is an allusion to the chance discovery of aventurine glass (goldstone) at some point in the 18th century. Goldstone is still manufactured today as an artificial imitation of the later discoveries aventurine quartz and aventurine feldspar ...
Feldspars make up about 60% of the Earth's crust [3] and 41% of the Earth's continental crust by weight. [5] [6] Feldspars crystallize from magma as both intrusive and extrusive igneous rocks [7] and are also present in many types of metamorphic rock. [8] Rock formed almost entirely of calcic plagioclase feldspar is known as anorthosite. [9]
The most common moonstone is of the orthoclase feldspar mineral adularia, named for an early mining site near Mt. Adular in Switzerland, now the town of St. Gotthard. [1] [better source needed] A solid solution of the plagioclase feldspar oligoclase +/− the potassium feldspar orthoclase also produces moonstone specimens.
Another variety more frequently used as a gemstone is the aventurine-feldspar or sun-stone found as reddish cleavage masses in gneiss at Tvedestrand in southern Norway; this presents a brilliant red to golden metallic glitter, due to the presence of numerous small scales of hematite oriented within the feldspar structure. [1]
Optical properties of common minerals Name Crystal system Indicatrix Optical sign Birefringence Color in plain polars Anorthite: Triclinic: Biaxial (-) 0.013
Additionally, "aventurine" glass is one of the few synthetic simulants to provide the eponym for the similar natural stones. The mineral name " aventurine " is used for forms of feldspar or quartz with mica inclusions that give a similar glittering appearance; the technical term for this optical phenomenon, " aventurescence ", is also derived ...