Heavy minerals in glacial material
The heavy minerals are generally regarded as comprising those minerals which have a high specific gravity, usually higher than that of the more common rock-forming minerals such as quartz and the feldpars. The weathering-resistant oxide and silicate minerals are usually used in heavy-mineral studies, while the more labile sulphide minerals have been studied in stream sediments but seldom in till deposits. The till samples for heavy-mineral surveys are most often taken with a shovel from the surficial part of till. When samples are needed from deeper parts a tractor excavator is used. Since most heavy minerals are already accessories in the bedrock, they occur sparsely in glacial sediments. It is thus necessary to concentrate the samples in order to facilitate the study of heavy minerals. Heavy-mineral concentrates are usually first analyzed chemically, by X-ray fluorescence spectrometry (XRF), atomic absorption spectrometry (AAS), optical emission spectrometry (OES) or instrumental neutron activation analysis.