Abstract
Magnetic properties of four groups of natural monomineralic clays were studied by means of thermomagnetic analysis, reflecting microscope, X-ray diffractometer, X-ray flourescence analyser and electron probe microanalyser. All samples were heated up to 700°C in air and in vacuum and it was found in many cases that a new magnetic phase appeared after heating. The new magnetic phase is thought to originate from colloid, amorphous iron impurities and/or hydroxidse of iron.
