...Lawrence R. Bernstein Abstract Monazite crystals from a 50 m wide quartz vein in Montgomery County, North Carolina show the alexandrite effect. The crystals are reddish-orange under incandescent light, yellow-orange in daylight, and light green under fluorescent light. The colors are due to narrow...

... of the crystal field environment giving rise to this rare optical effect. After most of our study was complete, Farrell and Newnham (1965) published the optical spectra of natural and synthetic alexandrite and have shown, as we had, quite clearly that the color and pleochroism are due to the presence of Cr...

... and the so-called alexandrite effect wherein the perceived color of a mineral changes with different lighting conditions (i.e., daylight vs. incandescent light). In this article we have collected ultraviolet/visible/near-infrared (UV-Vis-NIR) spectra of a gem-quality, synthetic Cr-bearing chrysoberyl crystal...

... of predominant dravite composition with 0.12 apfu Cr. For comparison a dark-green vanadium-bearing tourmaline from Tanzania (0.05 apfu V), which does not show such an effect, was also investigated. As established, the Usambara effect, by its nature, is closely related to the alexandrite effect, although...

... substituted in the X and Y sites of garnet's crystal structure provide a broad range of coloration, including red, green, yellow, pink, and orange ( Rossman 2009 ). Some garnets exhibit an alexandrite effect, i.e. their color changes with the lighting conditions ( Gübelin and Schmetzer 1982 ). Rare blue...

... samples fall into the lower range of natural alexandrites. According to their higher trace-element content, natural alexandrites from Hematita have slightly higher refractive indices and specific gravity. Iron has a restraining effect on Cr fluorescence ( Waychunas, 1988 ). The fluorescence of natural...

... formulation of matrix effects . Journal de Physique (Paris), Colloque , 45 ( 2 ), 17 – 20 . Powell R.C. Xi Lin Gang Xu Quarles G.J. Walling J.C. ( 1985 ): Spectroscopic properties of alexandrite crystals . Phys. Review B , 32 , 2788 – 2797 . Preinfalk C. Kostitsyn...

... ) obtains its distinctive ‘alexandrite effect’ colour change – from green-dark green in natural light to purplish-red in incandescent light – from a minor amount of Cr 3+ and/or Fe 3+ . In nature, these minor elements are most commonly derived from Cr-rich ultramafic rocks at the site of Be mineralization...

... . Scalvi R.M.F. Li M.S. Scalvi L.V.A. ( 2003 ) Annealing effects on optical properties of natural alexandrite . Journal of Physics: Condensed Matter , 15 , 7437 – 7443 . Schmetzer K. ( 1981 ) Zur Mineralogie ternärer Oxide im System BeO-MgO-Al 2 O 3 . Naturwissenschaften , 68...

..., another first-principles study investigated the effect of fluorine content on the elastic behavior of topaz and found that orthorhombic Pbnm symmetry has the lowest energy for F-topaz, but orthorhombic Pbn 2 1 is more appropriate for intermediate F/OH compositions ( Ulian and Valdre 2017...

... techniques are commonly employed to grow ruby, sapphire, chrysoberyl (alexandrite), and many crystals with a garnet structure (e.g. yttrium aluminum garnet, YAG). For those gems that melt incongruently—for example beryl—solution growth (in particular, under hydrothermal conditions) comes close...

... , 742 pp Kane RE ( 2009 ) Seeking low-cost perfection: Synthetic gems . Elements 5 : 169 - 174 Liu Y , Shigley JE , Fritsch E , Hemphill S ( 1994 ) The “alexandrite effect” in gemstones . Color Research and Application 19 : 186 - 191 Moses TM...

... , Žáček and Vrána, 2002 ). Alexandrite, a gemstone variety of chrysoberyl, is characterised by two distinct optical effects, including the alexandrite effect produced by Cr 3+ and V 3+ impurities and the cat's eye effect. Three principal lithological types of magmatic or metamorphic chrysoberyl...

... to Cr 3+ ). The maximums are shifted to the higher nm values, compare to alexandrite studied under the same conditions. That causes the absence of an alexandrite effect. In reflected light, mariinskite is gray with very weak bluish hue and green internal reflections. The mineral has very weak...

... of directional properties (while avoiding the complications of face indices). Part II deals mainly with individual gem species opening with two chapters on diamond, the first covering a general survey of diamond from the various regions of the world, before describing the effects on it of light and other...

.... Chrysoberyl is the only known mineral in the system. Its formula is commonly written as BeAl 2 O 4 , but Al 2 BeO 4 is more appropriate, because this form emphasizes the isostructural relationship to olivine ( Strunz 1966 ). The alexandrite-effect is due to impurities of Cr 3+ , which produces green color...

.... ( 1992 ) Alexandrite as a high-temperature pressure calibrant, and implications for the ruby-fluorescence scale . Journal of Applied Physics , 71 , 1579 – 1584 . Jovanić B.R. ( 2000 ) Effect of high pressure on fluorescence lifetime and position for R1 line in synthetic spinel MgAl 2 O 4...