| Amazonite | |
|---|---|
 Amazonite from Brazil | |
| General | |
| Category | Tectosilicate minerals |
| Group | Feldspar group |
| Series | Alkali feldspar series |
| Variety of | Microcline |
| Formula | KAlSi3O8 |
| Crystal system | Triclinic |
| Identification | |
| Color | Green, blue-green |
| Crystal habit | Prismatic |
| Cleavage | Perfect |
| Fracture | Uneven, splintery |
| Tenacity | Brittle |
| Mohs scale hardness | 6.0–6.5 |
| 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 |
| Ultravioletfluorescence | Weak; olive-green |
| Other characteristics |  Radioactive 14.05% (K) |
| References | [1][2][3]:214–215 |
Amazonite, also known asamazonstone,[4] is a greentectosilicatemineral, a variety of the potassium feldspar calledmicrocline.[4][5][6] Itschemical formula is KAlSi3O8,[1][7] which ispolymorphic toorthoclase.
The name is derived from theAmazon River, from which green stones were once believed to have been obtained, although it remains uncertain whether those stones were actually amazonite.[4] Although amazonite has been used for jewellery for more than three thousand years, as evidenced by archaeological finds in Middle and New Kingdom Egypt[8] and Mesopotamia, it is not mentioned by any ancient or medieval sources. It was first described as a distinct mineral in the 18th century.[9]
Green and greenish-blue varieties of potassium feldspars that are predominantly triclinic are designated as amazonite.[10] It has been described as a "beautiful crystallized variety of a bright verdigris-green"[11] and as possessing a "lively green colour".[4] It is occasionally cut and used as agemstone.[12]
Amazonite is a mineral of limited occurrence. In Bronze Age Egypt, it was mined in the southern Eastern Desert at Gebel Migif. In early modern times, it was obtained almost exclusively from the area ofMiass in theIlmensky Mountains, 50 miles (80 km) southwest ofChelyabinsk,Russia, where it occurs ingranitic rocks.[4]
Amazonite is now known to occur in various places around the world. Those places are, among others, as follows:
Australia:
China:
Libya:
Mongolia:
Ethiopia:
South Africa:
Sweden:
United States:
For many years, the source of amazonite's color was a mystery.[20] Some people assumed the color was due to copper becausecopper compounds often have blue and green colors.[20] A 1985 study suggests that the blue-green color results from quantities oflead and water in the feldspar.[20] Subsequent 1998 theoretical studies by A. Julg expand on the potential role of aliovalent lead in the color of microcline.[21]
Other studies suggest the colors are associated with the increasing content of lead,rubidium, andthallium 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.[10] A 2010 study also implicated the role of divalentiron in the green coloration.[7] These studies and associated hypotheses indicate the complex nature of the color in amazonite; in other words, the color may be the aggregate effect of several mutually inclusive and necessary factors.[9]
A 2021 study by the German Institut für Edelsteinprüfung (EPI) found that the amount of lead ions that leaked from an 11 g (0.39 oz) sample of amazonite into an acidic solution simulating saliva exceededEuropean 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 "crystal healing" practices such as inserting the mineral into drinking water bottles.[22]
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One or more of the preceding sentences incorporates text from a publication now in thepublic domain: Chisholm, Hugh, ed. (1911). "Amazon-stone".Encyclopædia Britannica. Vol. 1 (11th ed.). Cambridge University Press. p. 791.
Media related toAmazonite at Wikimedia Commons
Gemmological classifications by E. Ya. Kievlenko (1980), updated | |||||||||
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