Maxixe

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Maxixe beryl
Chemical composition Be3Al2(SiO3)6 Beryllium aluminum silicate
Crystal system Hexagonal
Habit Prismatic
Cleavage Poor, basal
Fracture Conchoidal to uneven
Hardness 7.5
Optic nature Uniaxial -
Refractive index 1.579 - 1.592
Birefringence 0.007
Dispersion Low, 0.0014
Specific gravity 2.69 - 2.8
Lustre Vitreous
Pleochroism Distinct

Maxixe (pron. Mah-she-she) is the almost Sapphire color variety of Beryl. It was discovered in 1917 in the Maxixe mine in the Piaui area south of Arassuahy, Minas Gerais, Brazil. Maxixe owes it's very unstable color due to natural irradiation which causes a color center that is most probably caused in the NO3 sites. When exposed to sunlight or temperatures above 100° C. it will rapidly loose its color, which can be restored by irradiation (gamma, x-ray or neutron) and annealing.
As of 1973 some dark-blue Beryls started appearing on the market again and research showed that the color was also due to irradiation (artificial), the color center in this case proved to be CO3. This new type was named "Maxixe-type" Beryl and like Maxixe it is a very unstable color. The starting color of these stones were yellow or green Beryls.
There are also bi-colored Maxixe-type Beryls (yellow/blue) and their color is attributed to artificial irradiation on specimens that have uneven distribution of impurities.

The impurities found in Maxixe and Maxixe-type Beryl are Cs, Zn, Li, Rb, B and high Fe content.