Rare earth minerals in the alluvials are contained in the rare earth phosphate minerals, monazite ([Ce, La, Y, Th]PO4) and xenotime (YPO4).  The term ‘Rare Earths’ refers to a group of 15 chemical elements, with similar properties and with atomic numbers ranging from 57-71.  Rare earths are also termed ‘lanthanides’, deriving from the transition element Lanthanum.  Yttrium is commonly included with the RE elements because it tends to occur in association with them due to its similar chemical properties.  The first four lanthanide elements, from Lanthanum to Neodymium are referred to as the ‘light’ RE elements (“LREE”), Samarium to Gadolinium are referred to as the ‘mid’ RE elements (“MREE”), while the remaining elements, Terbium to Lutetium plus Yttrium, comprise the Yttrium subgroup or ‘heavy’ RE elements (“HREE”).