Amazonite: Gemstone Information
The name amazonite appears to have evolved from the term ‘Amazon stone’ which, perhaps through confusion, was applied originally to another green mineral from that region as amazonite is not found anywhere in the Amazon basin.
Synonyms: Amazon stone; amazonstone; mother of emerald; green feldspar; microcline, Colorado Jade, and Amazon Jade. Amazonite is an opaque to translucent, blue to green, variety of microcline characterized by streaks of white exsolved albite. The colour has been attributed to three variables: lead, structural water and natural
radiation. Hoffmeister and Rossman (1985) proposed that while lead does indeed play a role in colouring amazonite, both natural radiation and structural water are necessary to produce chromophoric monovalent
or trivalent lead. The natural decay of potassium40 reduces Pb2+ to Pb1+, produces hydroxyl radicals that oxidize nearby oxygens to form hole centres and oxidizes Pb2+ to Pb3+. Comparison of color intensity with Pb concentration indicated no correlation. It has been suggested that if there is a higher degree of Al/Si disorder then green is the dominant colour. Heating will remove the blue–green colour. Use mainly as a gem material for beads, cabochons, the perfect cleavages making it somewhat unsuitable for carving. Reflections from incipient cleavages give polished surfaces a shimmering appearance.
• Crystal system: Triclinic
• Refractive index: α 1.514–1.529; β 1.518–1.533; γ 1.521–1.539 (Amazonite 1.522–1.530). Biaxial ve
• Birefringence: 0.008–0.010 (Amazonite 0.008)
• Pleochroism: Weak
• Density: 2.55–2.63 (Amazonite 2.56–2.58)
• Hardness: 6–6.5 (Amazonite 6.5)
• Dispersion: Weak
• Cleavage/fracture: Characteristic cleavages are prismatic perfect, intersecting at approximately 90°. Conchoidal to uneven fracture
• Optical effects: chatoyancy, asterism, colour change, ADR See moonstone
• Absorption Spectra (400–700 nm): Amazonite usually shows blanket absorption throughout the visible spectrum with a minimum absorption at 550 nm increasing towards both the red and violet
• Fluorescence: SWUV – microcline may fluoresce with a weak red or moderate blue colour, bluish white or pale greyish green. Microcline from Franklin, New Jersey, is reported as having a medium blue–grey fluorescence under SWUV. Some amazonite will fluoresce medium or weak red under SWUV. A yellowish green fluorescence has been reported under LWUV. Amazonite from Konso, Southern Nations Regional State, Ethiopia, fluoresces a deep maroon colour under SWUV whilst amazonite from Broken Hill, New South Wales, Australia, has been reported with unusual white/greenish fluorescence under SWUV.
Heat lessens fluorescence
• Simulant: Occasionally, in the past, initated by special types of glass
• Treatments: Amazonite – colour is lost on heating to over 300 °C and can be restored by irradiation if heating was insufficient ( 500 °C) to cause water loss.