Moonstone (gemstone)

Moonstone
General
Category Orthoclase variety
Formula
(repeating unit)		 (Na,K)AlSi308
Identification
Color Can be numerous colors, including blue, grey, white, pink, peach, green and brown, as well as colorless
Fracture uneven to conchoidal
Mohs scale hardness 6.0
Luster Opalescent
Streak white
Specific gravity 2.61
A small raw moonstone from an unknown area.

Moonstone is a sodium potassium aluminium silicate with the chemical formula (Na,K)AlSi3O8 and belongs to the feldspar group.

Etymology

Its name is derived from a visual effect, or sheen, caused by light diffraction within a micro-structure consisting of a regular of feldspar layers (lamellae).

History

Moonstone has been used in jewelry for millennia, including ancient civilizations. The Romans admired moonstone, as they believed it was born from solidified rays of the Moon.[1] Both the Romans and Greeks associated moonstone with their lunar deities. In more recent history, moonstone became popular during the Art Nouveau period; French goldsmith René Lalique and many others created a large quantity of jewelry using this stone.[2]

Geology

The most common moonstone is of the mineral adularia, named for an early mining site near Mt. Adular in Switzerland, now the town of St. Gotthard.[3] The plagioclase feldspar oligoclase also produces moonstone specimens. Moonstone is feldspar with a pearly and opalescent schiller.[3][4] An alternative name is hecatolite.[4]

Formation

Moonstone is composed of two feldspar species, orthoclase and albite. The two species are intermingled. Then, as the newly formed mineral cools, the intergrowth of orthoclase and albite separates into stacked, alternating layers. When light falls between these thin, flat layers, it scatters in many directions producing the phenomenon called adularescence.

Occurrence

Polished moonstone cabochon

Deposits of moonstone occur in Armenia (mainly from Lake Sevan), Australia, the Austrian Alps, Mexico, Madagascar, Myanmar, Norway, Poland, India, Sri Lanka[5] and the United States.[4]

The moonstone is the Florida State Gemstone; it was designated as such in 1970 to commemorate the Moon landings, which took off from Kennedy Space Center. Despite it being the Florida State Gemstone, it does not naturally occur in the state.[6]

References

  1. ↑ "Moonstone" American Gem Trade Association. Retrieved 21 January 2011.
  2. ↑ "Moonstone" International Colored Gemstone Association. Retrieved 26 April 2012.
  3. 1 2 Moonstone Gemological Information International Gem Society, Retrieved 01-05-15
  4. 1 2 3 Moonstone on Mindat.org
  5. ↑ "Moonstone" Encyclopædia Britannica, 2011. Web. 20 Jan. 2011.
  6. ↑ "Moonstone - Florida State Symbols". Florida Division of Historical Resource. Retrieved 1 Sep 2011.


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