Amazonite

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Amazonite
Amazonita1.jpeg
Amazonite from Brazil
General
Category Tectosilicate
Formula
(repeating unit)
KAlSi3O8
Crystal system Triclinic
Identification
ColorGreen, blue-green
Crystal habit Prismatic
Cleavage Perfect
Fracture Uneven, splintery
Tenacity Brittle
Mohs scale hardness6-6.5
Luster Vitreous
Streak White
Diaphaneity Translucent, opaque
Specific gravity 2.56-2.58
Refractive index 1.522-1.530
Birefringence -0.008
Pleochroism Absent
Dispersion None
Ultraviolet fluorescence Weak; olive-green
Other characteristics Radioactive.svg Radioactive 14.05% (K)
References [1] [2] [3] :214-215

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.

Contents

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[ clarification needed ] 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 that 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[ 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. [4]

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

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]

Health

A 2021 study by the German Institut für Edelsteinprüfung (EPI) found that the amount of lead that leaked from a 11 g (0.39 oz) sample of Amazonite into an acidic solution simulating saliva exceeded European Union standard DIN EN 71-3:2013's recommended amount by five times. This experiment was to simulate a child swallowing Amazonite, and could also apply to new wellness practices such as inserting the mineral into oils or drinking water for days. [18]

Related Research Articles

Amethyst Mineral, quartz variety

Amethyst is a violet variety of quartz. The name comes from the Koine Greek αμέθυστος amethystos from α- a-, "not" and μεθύσκω methysko / μεθώ metho, "intoxicate", a reference to the belief that the stone protected its owner from drunkenness. The ancient Greeks wore amethyst and carved drinking vessels from it in the belief that it would prevent intoxication.

Beryl Gemstone: beryllium aluminium cyclosilicate

Beryl ( BERR-əl) is a mineral composed of beryllium aluminium cyclosilicate with the chemical formula Be3Al2Si6O18. Well-known varieties of beryl include emerald and aquamarine. Naturally occurring, hexagonal crystals of beryl can be up to several meters in size, but terminated crystals are relatively rare. Pure beryl is colorless, but it is frequently tinted by impurities; possible colors are green, blue, yellow, and red (the rarest). Beryl can also be black in color. It is an ore source of beryllium.

Quartz Mineral made of silicon and oxygen.

Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO2. Quartz is the second most abundant mineral in Earth's continental crust, behind feldspar.

Tourmaline Cyclosilicate mineral group

Tourmaline is a crystalline boron silicate mineral compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is classified as a semi-precious stone. This gemstone can be found in a wide variety of colors.

Feldspar Group of rock-forming minerals

Feldspars are a group of rock-forming aluminium tectosilicate minerals, containing sodium, calcium, potassium or barium. The most common members of the feldspar group are the plagioclase (sodium-calcium) feldspars and the alkali (potassium-sodium) feldspars. Feldspars make up about 60% of the Earth's crust, and 41% of the Earth's continental crust by weight.

Prehnite

Prehnite is an inosilicate of calcium and aluminium with the formula: Ca2Al(AlSi3O10)(OH)2. Limited Fe3+ substitutes for aluminium in the structure. Prehnite crystallizes in the orthorhombic crystal system, and most often forms as stalactitic or botryoidal aggregates, with only just the crests of small crystals showing any faces, which are almost always curved or composite. Very rarely will it form distinct, well-individualized crystals showing a square-like cross-section, including those found at the Jeffrey Mine in Asbestos, Quebec, Canada. Prehnite is brittle with an uneven fracture and a vitreous to pearly luster. Its hardness is 6-6.5, its specific gravity is 2.80-2.90 and its color varies from light green to yellow, but also colorless, blue, pink or white. In April 2000, rare orange prehnite was discovered in the Kalahari Manganese Fields, South Africa. Prehnite is mostly translucent, and rarely transparent.

Orthoclase Tectosilicate mineral found in igneous rock

Orthoclase, or orthoclase feldspar (endmember formula KAlSi3O8), is an important tectosilicate mineral which forms igneous rock. The name is from the Ancient Greek for "straight fracture," because its two cleavage planes are at right angles to each other. It is a type of potassium feldspar, also known as K-feldspar. The gem known as moonstone (see below) is largely composed of orthoclase.

Microcline

Microcline (KAlSi3O8) is an important igneous rock-forming tectosilicate mineral. It is a potassium-rich alkali feldspar. Microcline typically contains minor amounts of sodium. It is common in granite and pegmatites. Microcline forms during slow cooling of orthoclase; it is more stable at lower temperatures than orthoclase. Sanidine is a polymorph of alkali feldspar stable at yet higher temperature. Microcline may be clear, white, pale-yellow, brick-red, or green; it is generally characterized by cross-hatch twinning that forms as a result of the transformation of monoclinic orthoclase into triclinic microcline.

Turquoise Opaque, blue-to-green mineral

Turquoise is an opaque, blue-to-green mineral that is a hydrated phosphate of copper and aluminium, with the chemical formula CuAl6(PO4)4(OH)8·4H2O. It is rare and valuable in finer grades and has been prized as a gemstone and ornamental stone for thousands of years owing to its unique hue. Like most other opaque gems, turquoise has been devalued by the introduction onto the market of treatments, imitations and synthetics.

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Teller County is a county located in the U.S. state of Colorado. As of the 2010 census, the population was 23,350. The county seat is Cripple Creek, and the most populous city is Woodland Park.

Albite Mineral, Na-feldspar, Na-silicate, tectosilicate

Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. It represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula NaAlSi
3
O
8
. It is a tectosilicate. Its color is usually pure white, hence its name from Latin, albus. It is a common constituent in felsic rocks.

Perthite

Perthite is used to describe an intergrowth of two feldspars: a host grain of potassium-rich alkali feldspar (near K-feldspar, KAlSi3O8, in composition) includes exsolved lamellae or irregular intergrowths of sodic alkali feldspar (near albite, NaAlSi3O8, in composition). Typically, the host grain is orthoclase or microcline, and the lamellae are albite. If sodic feldspar is the dominant phase, the result is an antiperthite and where the feldspars are in roughly equal proportions the result is a mesoperthite.

Spessartine

Spessartine, sometimes mistakenly referred to as spessartite, is a nesosilicate, manganese aluminium garnet species, Mn2+3Al2(SiO4)3. The mineral spessartine should not be confused with a type of igneous rock (a lamprophyre) called spessartite.

Pikes Peak granite

The Pikes Peak granite is a 1.08 billion year old widespread geologic formation found in the central part of the Front Range of Colorado. It is a coarse-grained pink to light red syenogranite with minor gray monzogranite, and it has a distinctive brick-red appearance where it outcrops. The granite gets its name from the 14,115-foot (4,302 m) Pikes Peak, which is made up almost entirely of this rock.

Sunstone

Sunstone is a plagioclase 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.

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Cathedral Peak Granodiorite

The Cathedral Peak Granodiorite (CPG) was named after its type locality, Cathedral Peak in Yosemite National Park, California. The granodiorite forms part of the Tuolumne Intrusive Suite, one of the four major intrusive suites within the Sierra Nevada. It has been assigned radiometric ages between 88 and 87 million years and therefore reached its cooling stage in the Coniacian.

Mineralogy of the Pikes Peak Region

The Pikes Peak region is renowned for its rare mineral specimens. It is a favorite collecting area for rock hounds and serious collectors alike. Scientists from around the world come to Colorado to study the minerals of this region. Because the granite covers a large portion of the Colorado Front Range, there are good mineral collecting areas scattered all over the Pikes Peak region. The collecting localities range from near Colorado Springs on the south to just west of Denver on the north.

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References

  1. 1 2 Walter, Schumann (1997). Gemstones of the world (Rev. & expanded ed.). New York: Sterling Pub. Co. p.  164. ISBN   0806994614 via Internet Archive.
  2. "Radioactive Gems : ClassicGems.net". ClassicGems.net. Archived from the original on 2021-02-11. Retrieved 2021-08-13.
  3. 1 2 3 4 5 6 7 8 9 10 11 Schlegel, Dorothy McKenney (1957). "Gem Stones of the United States". Geological Survey Bulletin. United States Government Publishing Office (1042-G) via Google Books.
  4. 1 2 3 4 5 6 Wikisource-logo.svg 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. Archived from the original on 2021-03-01. Retrieved 2018-08-24.
  6. 1 2 "Amazonite: Amazonite mineral information and data". mindat.org. Archived from the original on 14 May 2021. Retrieved 13 April 2017.
  7. 1 2 Mikhail Ostrooumov, Amazonite: Mineralogy, Crystal Chemistry, and Typomorphism (Elsevier, 2016), p. 1-12.
  8. 1 2 3 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. Wikisource-logo.svg 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. 1 2 3 4 "Amazonite from South Africa". www.mindat.org. Retrieved 2020-05-25.
  15. 1 2 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. 1 2 3 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.
  18. "Lead in Amazonite - Caution". Institut für Edelsteinprüfung. April 22, 2021. Archived from the original on March 7, 2021. Retrieved August 13, 2021.

Further reading

Commons-logo.svg Media related to Amazonite at Wikimedia Commons