Amazonite

Amazonite, also known as Amazonstone,[4] is a green tectosilicate mineral, a variety of the potassium feldspar called microcline.[4][5] Its chemical formula is KAlSi3O8,[1][6] which is polymorphic to orthoclase.

Amazonite
Amazonite from Brazil
General
CategoryTectosilicate
Formula
(repeating unit)		KAlSi3O8
Crystal systemTriclinic
Identification
ColorGreen, blue-green
Crystal habitPrismatic
CleavagePerfect
FractureUneven, splintery
TenacityBrittle
Mohs scale hardness6-6.5
LusterVitreous
StreakWhite
DiaphaneityTranslucent, opaque
Specific gravity2.56-2.58
Refractive index1.522-1.530
Birefringence-0.008
PleochroismAbsent
DispersionNone
Ultraviolet fluorescenceWeak; olive-green
Other characteristics Radioactive 14.05% (K)
References[1][2][3]:214-215

Its name is taken from that of the Amazon River, from which green stones were formerly obtained, though it is unknown whether those stones were amazonite.[4] Although it has been used for over two thousand years, as attested by archaeological finds in Egypt and Mesopotamia, no ancient or medieval authority mentions it. It was first described as a distinct mineral only in the 18th century.[7]

Green and greenish-blue varieties of potassium feldspars which are predominantly triclinic are designated as amazonite.[8] It has been described as a "beautiful crystallized variety of a bright verdigris-green"[9] and as possessing a "lively green colour."[4] It is occasionally cut and used as a gemstone.[10]

Occurrence

Amazonite is a mineral of limited occurrence. Formerly it was obtained almost exclusively from the area of Miass in the Ilmensky Mountains, 50 miles southwest of Chelyabinsk, Russia, where it occurs in granitic rocks.[4]

Amazonite is now known to occur in various places around the globe. Those places are, among others;

China:

Libya:

Mongolia:

South Africa

United States:

Color

For many years, the source of amazonite's color was a mystery.[16] Some people assumed the color was due to copper because copper compounds often have blue and green colors.[16] A 1985 study suggest that the blue-green color results from quantities of lead and water in the feldspar.[16] Subsequent 1998 theoretical studies by A. Julg expand on the potential role of aliovalent lead in the color of microcline.[17]

Other studies suggest the colors are associated with the increasing content of lead, rubidium, and thallium ranging in amounts between 0.00X and 0.0X in the feldspars, with even extremely high contents of PbO, lead monoxide, (1% or more) known from the literature.[8] A recent 2010 study also implicated the role of divalent iron in the green coloration.[6] These studies and associated hypotheses indicate the complex nature of the color in amazonite, in other words the aggregate effect of several mutually inclusive and necessary factors.[7]

References
  1. Walter, Schumann (1997). Gemstones of the world (Rev. & expanded ed.). New York: Sterling Pub. Co. p. 164. ISBN 0806994614 – via Internet Archive.
  2. http://www.classicgems.net/info_Radioactive.htm
  3. Schlegel, Dorothy McKenney (1957). "Gem Stones of the United States". Geological Survey Bulletin. United States Government Publishing Office (1042-G) – via Google Books.
  4.  One or more of the preceding sentences incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Amazon-stone". Encyclopædia Britannica. 1 (11th ed.). Cambridge University Press. p. 791.
  5. "Amazonite gemstone information". gemdat.org. Retrieved 2018-08-24.
  6. "Amazonite: Amazonite mineral information and data". mindat.org. Retrieved 13 April 2017.
  7. Mikhail Ostrooumov, Amazonite: Mineralogy, Crystal Chemistry, and Typomorphism (Elsevier, 2016), p. 1-12.
  8. Pivec, E.; Ševčik, J.; Ulrych, J. (December 1981). "Amazonite from the alkali granite of the Avdar Massif, Mongolia". TMPM Tschermaks Petr. Mitt. 28 (4): 277–283. Bibcode:1981TMPM...28..277P. doi:10.1007/BF01081855.
  9.  One or more of the preceding sentences incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Microcline". Encyclopædia Britannica. 1 (11th ed.). Cambridge University Press. p. 380.
  10. "Common Minerals of Virginia". Virginia Department of Mines, Minerals and Energy. Commonwealth of Virginia. Retrieved 5 July 2019.
  11. Yang, Jianye; Zhao, Lei; Zhang, Weiguo (April 2014). "The Geochemical Effect of Lanthanides: Its Types and Application for Magmatic Rocks—A New Method to Semi-Quantitatively Determine Strength of Magmatic Fluid Complexation and Fractional Crystallization" (PDF). Journal of Earth Science. China University of Geosciences (Wuhan). 25 (2): 252–262. doi:10.1007/s12583-014-0420-z. ISSN 1674-487X. S2CID 54836739.
  12. Sihai, Liu; Changzhi, Wu; Lianxing, Gu; Zunzhong, Zhang; Junhua, Tang; Guangrong, Li; Ruxiong, Lei; Chuansheng, Wang (2008). "中天山白石头泉岩体年代学、岩石成因及构造意义" [Geochronology, petrogenesis and tectonic significances of the Baishitouquan pluton in Middle Tianshan, Northwest China]. Acta Petrologica Sinica (in Chinese). Beijing: China Science Publishing & Media Ltd. 24 (11): 2720. ISSN 1000-0569.
  13. Suayah, Ismail B.; Miller, Jonathan S.; Miller, Brent V.; et al. (April 2006). "Tectonic significance of Late Neoproterozoic granites from the Tibesti massif in southern Libya inferred from Sr and Nd isotopes and U–Pb zircon data". Journal of African Earth Sciences. 44 (4–5): 564. Bibcode:2006JAfES..44..561S. doi:10.1016/j.jafrearsci.2005.11.020. ISSN 1464-343X. S2CID 26947582.
  14. "Amazonite from South Africa". www.mindat.org. Retrieved 2020-05-25.
  15. Penick, D. Allen Jr.; Sweet, Palmer C. (May 1992). "Mineral collecting sites in Virginia" (PDF). Virginia Minerals. Charlottesville, Virginia: Virginia Department of Mines, Minerals, and Energy. 38 (2): 10–12. Archived from the original (PDF) on 24 April 2012.
  16. Hoffmeister and Rossman (1985). "A spectroscopic study of irradiation coloring of amazonite; structurally hydrous, Pb-bearing feldspar" (PDF). American Mineralogist. 70: 794–804 – via Mineralogical Society of America.
  17. Julg, A. (February 1998). "A theoretical study of the absorption spectra of Pb+ and Pb3+ in site K+ of microcline: application to the color of amazonite". Physics and Chemistry of Minerals. Springer-Verlag. 25 (3): 229–233. Bibcode:1998PCM....25..229J. doi:10.1007/s002690050108. ISSN 1432-2021. S2CID 95011489.

Further reading
  • Perl, Richard M. (1972). Colorado Gem Trails: And Mineral Guide. Swallow Press. ISBN 978-0-8040-0956-0.

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