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Amazonite

Amazonite
Photo of a turquoise mineral with beige microcline speckled within it
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
References[1][2]:214-215

Amazonite, also known as Amazonstone,[3] is a green tectosilicate mineral, a variety of the potassium feldspar called microcline.[3][4] Its chemical formula is (KAlSi3O8),[1][5] which is polymorphic to Orthoclase.

Its name is taken from that of the Amazon River, from which certain green stones were formerly obtained, but it is doubtful whether green feldspar occurs in the Amazon area.[3] 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.[6]

Because of its bright green color when polished, amazonite is sometimes cut and used as a cheap gemstone, although it is easily fractured, and loses its gloss due to its softness.[citation needed]

Occurrence

Amazonite is a mineral of limited occurrence. Formerly[when?] 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.[3]

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

China:

Libya:

United States:

Color

For many years, the source of amazonite's color was a mystery.[11] Some people assumed the color was due to copper because copper compounds often have blue and green colors.[11] A 1985 study suggest that the blue-green color results from small quantities of lead and water in the feldspar.[11]

Gallery

Notes

  1. ^ a b Walter, Schumann (1997). Gemstones of the world (Rev. & expanded ed.). New York: Sterling Pub. Co. p. 164. ISBN 0806994614 – via Internet Archive.
  2. ^ a b c d e f g h i j k Schlegel, Dorothy McKenney (1957). "Gem Stones of the United States". Geological Survey Bulletin. United States Government Publishing Office (1042-G) – via Google Books.
  3. ^ a b c d e  One or more of the preceding sentences incorporates text from a publication now in the public domainChisholm, Hugh, ed. (1911). "Amazon-stone" . Encyclopædia Britannica. 1 (11th ed.). Cambridge University Press. p. 791.
  4. ^ "Amazonite gemstone information". gemdat.org. Retrieved 2018-08-24.
  5. ^ "Amazonite: Amazonite mineral information and data". mindat.org. Retrieved 13 April 2017.
  6. ^ Mikhail Ostrooumov, Amazonite: Mineralogy, Crystal Chemistry, and Typomorphism (Elsevier, 2016), .
  7. ^ 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. 25 (2): 252–262. doi:10.1007/s12583-014-0420-z. ISSN 1674-487X.
  8. ^ 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. 24 (11): 2720. ISSN 1000-0569.
  9. ^ 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" (PDF). Journal of African Earth Sciences. 44 (4–5): 564. doi:10.1016/j.jafrearsci.2005.11.020. ISSN 1464-343X – via Semantic Scholar.
  10. ^ a b 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 (No. 2): 10–12. Archived from the original (PDF) on 24 April 2012.
  11. ^ a b c 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.

References