Elemental and Crystalline Phase Analysis for Mineral Composition by XRF and XRD
Wavelength-Dispersive XRF Analysis
The XRF elemental analysis is performed first, because knowing the elemental composition is a great aid in guiding which of many tens of thousands of crystalline chemical phases may be present in a potentially very complex XRD spectrum. After grinding the sample to a fine powder, it was placed in a plastic cup with a thin polypropylene film covering the 29 mm aperture in the bottom of the cassette into which the plastic cup was inserted. A solid sample capable of supporting itself over the 29 mm aperture would be analyzed in vacuum, but a powder sample is analyzed in helium. Our Thermo Scientific ARL PERFORM’X 1500 sequential XRF spectrometer detects and measures the elements from sodium through uranium when operated under helium atmosphere. The results in weight percent are given below.
Sx is sulfur as sulfate and Px is phosphorus as phosphate.
Mineral Composition XRD Analysis to Identify Crystalline Chemical Phases
A finely ground sample from the unknown mineral was prepared for analysis in our Rigaku MiniFlex 6G XRD instrument.
Lizardite, a mineral in the serpentine subgroup, is the predominant phase in the gravel material. The Clinochlore and Kaolinite phases are clay minerals of the phyllosilicate group of silicate minerals. The iron manganese silicon and the cobalt iron phases that fit the data are questionable because they are not oxidized. The concentration of manganese is fairly consistent with the XRF result. While cobalt is found by XRF, there is too little cobalt for the amount implied by the XRD fit. So the cobalt iron should be considered improbable and the iron manganese silicon very questionable. Between them, they leave 3.72 weight percent of the composition unknown.
