Evaluation of a Magnetic Separation Index Test to Determine the Gravimetric Glauconite Content of Clean Sands

This work presents a practical glauconite content test using magnetic separation to determine gravimetric (mass) content of intact glauconite-bearing grains to in clean sand, which can be used to represent the crushable proportion of a soil sample. The test provides an additional level of soil characterization for glauconite, for which the currently used methods measure either the glauconite mineral content or provide only an estimate of glauconite grain content using a microscope. The simple test was designed to be used in the field or in a laboratory on an ocean-going vessel, relevant to offshore energy infrastructure. It uses a rare-earth magnet and a sample jar to determine the concentration by mass of glauconite grains, which are green, paramagnetic, and friable. They tend to crush under load, which alters its soil behavior, transitioning from coarse grained to fine grained. Typical measurement methods for determining glauconite content are visual grain counting, X-ray diffraction, and tabletop electromagnetic separators. None of these methods can measure the gravimetric content of glauconite-bearing grains in a soil and they can be costly to run or require expert knowledge to use. The variability in the gravimetric concentration with this method is presented by testing a series of prepared samples with Ottawa sand and glauconite magnetically collected from the Poricy formation. A comparison between the magnetic separation test, digital image analysis, and X-ray diffraction testing is provided. It was found that, for the soil tested, the magnetic separation test has a variability within 0.4 % of the actual concentration in prepared samples. These results show that the magnetic separation test is an effective and efficient option for determining the gravimetric glauconite concentration of a soil sample.