Magnetic properties of natural materials

Abstract

The main impetus for the study of the magnetic properties of rocks and sediments came with the realisation that many natural materials record valuable information about the Earth’s ancient field by retaining a magnetic remanence acquired close to the time of their formation. The majority of magnetic studies of natural samples have thus been carried out by palaeomagnetists investigating natural remanent magnetisations. These studies have involved many rock types spanning all ages, and collected from all parts of the world. In association with these researchers into the Earth’s fossil magnetism, studies of synthetic materials have also been carried out. These are often referred to as rock magnetic studies (Nagata 1953). They have concentrated on providing background information of use to the palaeomagnetist, and have dealt mainly with natural iron minerals commonly capable of carrying a stable remanence, such as haematite and the titanomagnetites (e.g. Day et al. 1977, Bailey ... Dunlop 1983). A major endeavour of rock magnetists has been to elucidate the intricacies of thermoremanent magnetisation through laboratory studies of synthetic samples.

Walking around this little island (of Chaul)... a wonderful thing happened to me... placing the needle on top of a big boulder... the rose turned… it occurred to me that such a strange fact was due to the quality and nature of the rock.

Extract from log book of Joao de Castro 1538