Powder XRD analysis and Rietveld based quantification approaches for proving of moganite in silica natural samples

Powder XRD approaches are applied for proving of moganite in an agate from Lozevo village (Shumen region). Moganite associates with silica minerals – quartz (quartzine and chalcedony), opal-CT and opal-A, all being characteristic for agates. Quartz and moganite display similar structures and thus the powder XRD pattern of moganite significantly overlaps with that of quartz and distinguishing of moganite is difficult. However, some of its diffraction peaks are well observed – with inter-planner spacings (d) 4.43 Å, 3.388 Å, 3.116 Å. The presence of moganite is proved in the agate of study in all its zones. The applied XRD quantification by use of full-pattern Rietveld-based refinement showed moganite quantities from 21 to 31 wt% in the quartzine layers of the agate, 18.57 wt% in the chalcedony zone, and only 1.72 wt% in the quartz shell. The results of these XRD approaches may serve in reconstruction of mineral forming in silica environment.