Amazonite
Green silicate mineral / From Wikipedia, the free encyclopedia
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Amazonite, also known as amazonstone,[4] is a green tectosilicate mineral, a variety of the potassium feldspar called microcline.[4][5][6] Its chemical formula is KAlSi3O8,[1][7] which is polymorphic to orthoclase.
Amazonite | |
---|---|
General | |
Category | Tectosilicate |
Formula (repeating unit) | 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 |
Ultraviolet fluorescence | Weak; 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 jewellery for well over three thousand years, as attested by archaeological finds in Middle and New Kingdom Egypt[8] and Mesopotamia, no ancient or medieval authority mentions it. It was first described as a distinct mineral only 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 a gemstone.[12]