Celestine

Celestite, SrSO4, also called celestine, as well as the closely related ,materials anhydrite, CaSO4, also called vulpinite (Webster, p. 298), and barite, BaSO4, are soft sulfates which occur at times with attractive violet or blue colors. Heating to as little as 200�C causes these colors to fade, as also sometimes happens on exposure to light. Irradiation restores or produces the blue or violet color, sometimes in a banded form; the color may be stable to light or may fade, depending on the nature of the material (Przibram and Caffyn, 1956; Pough, 1957). In celestite there are several color centers involved, including SO-3, SO-2 and O-, all stabilized by a potassium impurity (Bernstein, 1979) � Nassau (1984) 3 to 3.5Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references 3.90 to 4.00Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references BrittleHerve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) Very brittle PerfectArthur Thomas, Gemstones (2009) UnevenArthur Thomas, Gemstones (2009) Sensitive to heatHerve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) 1.619 to 1.635Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references Biaxial/+Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references 0.004 to 0.012Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references Weakly trichroicArthur Thomas, Gemstones (2009) NilArthur Thomas, Gemstones (2009) Bluish-white, colourless, seldom reddish, greenWalter Schumann, Gemstones of the world (2001) More from other references TransparentMichael O?Donoghue, Gems, Sixth Edition (2006) More from other references VitreousWalter Schumann, Gemstones of the world (2001) More from other references Inert to weak fluorescence of body color (possible phosphorescence)Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references OrthorhombicHerve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) More from other references TabularMichael O?Donoghue, Gems, Sixth Edition (2006) More from other references Liquid inclusions, partially healed fractures - Blue Chart Gem Identification, Herve Nicolas Lazzarelli, 2010, p 5 Celestine information at mindat.org Namibia  Gems, Sixth Edition, Michael O’Donoghue, 2006, p. 396