Scales are deposits/coatings which form on the surface of another material, e.g. metals or rocks. To give you an idea of the variety of these materials some of the phases we have encountered in scales include, calcite, Mg-calcite, aragonite, Sr-Ca-carbonate, dolomite, siderite, gypsum, anhydrite, barite, Sr-barite, celestine, halite, berthierine, pyrite, and sphalerite although this list is not exhaustive. Clearly various carbonates and sulphates are common, and often they are non-stoichiometric.
X-ray diffraction (XRD) is the primary technique for the identification of scales. Precise measurement of peak positions can also give information on the solid solution compositions of non-stoichiometric scale phases, such as an estimation of the Sr-content of barite.