What cause Amazonite stone beads blue color

Amazonite is a popular gemstone usually varies in color from yellow-green to blue green and may also exhibit fine white streaks.  It was named after Amazon River, from which certain green stones were formerly obtained, however it is doubtful whether Amazonite occurs in the Amazon area. 

Amazonite is green to blue-green variety of Microcline.  Microcline (KAlSi₃O₈) may be clear, white, pale-yellow, brick-red, or green color depends on the impurities which contain. Common Impurities inside Microcline are Fe, Ca, Na, Li, Cs, Rb, H₂O, Pb.   The source of amazonite’s color was uncertain for years, and many assumed the color was due to copper, which often produces blue and green colors in gems and minerals.  However, studies [1] suggest that the blue-green color caused by an elevated content of Pb and water in the Microcline. In the past two to three decades, some inconsistencies with this possible correlation have become apparent.  Analyses by Hoffmeister and Rossman (1985) determined that some samples of green amazonite did indeed have a high lead concentration, whereas some non-green samples of microcline also had unexpectedly high lead concentrations. They propose that while lead does indeed play a role in coloring amazonite, both natural radiation and structural water are necessary to produce monovalent or trivalent lead for color of amazonite. Therefore the color of amazonite could possibly be due to three variables: lead, water and a form of ionizing radiation.  More recent studies [2] suggest that the green color would arise from the ion Pb⁺, whereas the blue one would be attributed to the ion Pb³⁺. Thus the blue-green color is due to mixture of Pb⁺ and Pb³⁺.

Amazonite often has white lines or alternating streaks mixed in, and can have uneven color distribution. A deep forest-green color is most preferred, but Amazonite gemstones can also be light green and bluish-green.  Grayish-green and very faint green stones also exist, but are not commonly used as gemstones.  

Sunlight can sometimes enrich the color of genuine amazonite.  Amazonite’s color is lost on heating to over 300°C and can be restored by irradiation if heating was insufficient (<500°C) to cause water loss. It has a hardness range of 5 to 6 on the Mohs Scale.  Care should be handled with Amazonite as it is sensitive to pressure and can easily crack or chip. 

Because of its bright green or blue-green color when polished, amazonite is sometimes cut and used as gemstone beads, although it is easily fractured.  You will not see amazonite very often in the current market. It makes some very pleasing jewelry items but is kind of hard to find.

Amazonite is an inexpensive gemstone is most often used in stone beads with different shapes:  round, coin, oval, square, pillow, cube, tube, et al. With Amazonite beads in your favorite color and shape, you even can create your own unique piece of Amazonite jewelry, and with plenty of opportunity to customize to fit your unique style. There are plenty of low-cost Amazonite beads available through online store and be sure to check out the discounted Amazonite beads first to start your design.

Reference:

[1] Brightwell, Stephanie, 1999; "Coloration due to Lead Levels in Blue microcline Feldspar (Amazonite) from the Morefield Pegmatite, Amelia, Virginia",

[2] Julg, A. (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 25, 229-233.