Abstract

Murat Hatipoğlu^1,2*, Yaşar Kibici³, Gürsel Yanık³, Cafer Özkul³, Yasemin Yardımcı¹

DOI : http://dx.doi.org/10.13005/ojc/310104

The strata that include the fine purple opal formations examined in this paper from the magmagenetic hydrothermal dis solutions. The opals are locally known as Gevrekseydi purple opals. These opal-bearing strata are deposited in volcanic lavas and tuffs in the Seyitömer-Kütahya region of western Turkey. The purple opals are common-type and attractive gem-quality, and they are sold on the worldwide gem markets. We conducted mineralogical investigations to clarify their silica building components, measure their nano-size, and determine their origins. The opals are an opal-CT (opal-cristobalite/tridymite)- type silica polymorph with the variable number of cristobalite and tridymite layers. The cristobalite and tridymite stacking sequences were evaluated in terms of maturation, crystallite size, and genesis of the opaline silica material. These sequences are modelled using X-ray diffraction patterns. The relationship between the crystallite size and full width at half maximum values of the Gevrekseydi purple opals were also examined using X-ray diffraction patterns. The crystallite sizes were found to be L=17 nm for the main opal-CT peak (4.09 Å), L=23 nm for the shoulder opal-CT peak (4.29 Å), and L=27 nm for the opal-CT/C peak (2.51 Å). Given the relationship between the crystallite size and maturation of opal-CT, the Gevrekseydi volcanic common purple opals are most likely in a stage of early to mid maturation

Gevrekseydi common purple opals; XRD; Opal-CT; Kütahya-Turkey

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