Color and genesis of californite from Pakistan: insights from μ-XRF mapping, optical spectra and X-ray photoelectron spectroscopy

Abstract

four californite samples from pakistan with yellowish-green, green and reddish-brown colors were investigated by combining the methods of μ-XRf mapping, XRD, Raman spectra, optical spectra, epMA and XpS. the results show that the californite is composed mainly of microcrystalline vesuvianite and smaller amounts of clinochlore. Based on the distribution of the clinochlore, the californite can be divided into three types. the gem-quality californite is composed of microcrystalline vesuvianite and has a translucent appearance. the ordinary-quality californite contains microcrystalline vesuvianite as well as clinochlore, and it has an opaque appearance. the transitional-type has properties that are intermediate between those of gem-and ordinary-quality californite. octahedrally coordinated iron and chromium in the clinochlore reduce the transparency and contribute to the opaque green and yellowish-green colors of the californite. At sites where there is no clinochlore, cr 3+ in the octahedrally coordinated site Y3 of the vesuvianite is mainly responsible for the green tone of the californite, fe 3+ and Mn 3+ at the Y3 site contribute mainly to the yellowish-green and reddish-brown colors, respectively. the fe 2+ → fe 3+ charge transfer also occurs in vesuvianite and partly influences the appearance of the californite. the actual color of californite that lacks clinochlore is due to the synergy of cr 3+ , fe 3+ and Mn 3+ crystal field transfers at the octahedral site Y3 as well as the Fe 2+ → fe 3+ charge transfer in the vesuvianite. Vesuvianite in the californite can be assigned to the P4/n space group, and the occurrence of clinochlore reflects the fact that the californite from Pakistan formed under mediumgrade metamorphic conditions at temperatures of ~300-500 °C. The content of clinochlore provides a basis for grading the quality of the californite.Californite usually refers to a microcrystalline interlocking mineral growth with vesuvianite as the major constituent. Because of its similar appearance to jadeite, californite is often considered as jadeite, and it is commonly known as golden-green jade in Chinese jewelry market. Vesuvianite is an ortho-disilicate mineral with the general formula X 18 X4Y1Y2 4 Y3 8 T 0-5 Si 18 O 68 (O, OH, F) 10 , where the X and X4 sites are occupied by Ca, Na and rare earth elements (REE); the Y1 site by Cu 2+ , Mn 3+ , Fe 2+ and Al 3+ ; and the Y2 and Y3 sites usually by Al 3+ 1-8 . As previously reported, elements substituting at the X4, Y1, Y3 and T sites have a great influence on the appearance of vesuvianite, a vesuvianite crystal may appear gold to deep red to opaque brown-black when some of Ca at the X4 site has been substituted by REE, and the intensity of the vesuvianite color increases with increasing REE content 9 . Mn 3+ and Cu 2+ can replace Fe 3+ , Mg 2+ , Al 3+ and Fe 2+ at the square pyramidal coordination site Y1 and cause the vesuvianite crystal to present yellow or dark red appearance with a lilac hue 5,6,10,11 . Cr 3+ at the octahedrally coordinated site Y3 is r...

Vivianite and Its Oxidation Products in Mammoth Ivory and Their Implications to the Burial Process

“…The peaks at around 711.7 and 710.1 eV are due to the octahedral coordination of Fe 3+ and Fe 2+ , respectively. The satellite peaks of Fe 3+ and Fe 2+ occur in the range of 715.4–716.6 and 713.4–713.8 eV . The spectra of Fe (2p) indicate the distributions and relative contents of vivianite, metavivianite, and santabarbaraite.…”

“…The satellite peaks of Fe 3+ and Fe 2+ occur in the range of 715.4−716.6 and 713.4−713.8 eV. 42 The spectra of Fe (2p) indicate the distributions and relative contents of vivianite, metavivianite, and santabarbaraite.…”

Preparation of Ce/ferroferric oxide/food waste‐derived biochar for aqueous Cr(VI) adsorption

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