Class of elements: Lanthanoids
Lanthanum is a member of the lanthanoid group of elements (IUPAC terminology). Lanthanoids were previously known as lanthanides and, together with scandium and yttrium, they are commonly referred to as "rare earth" or "rare earth elements". Despite the use of the term "rare" these elements are actually fairly abundant in nature, although "rare" when compared to "common" earths such as lime or magnesia. Cerium for example is the 26th most abundant element in the Earth's crust and neodymium is more abundant than gold. Thulium (the least common naturally-occurring lanthanoid) is even more abundant than iodine.
Lanthanum forms a very strong bond with oxidized anions, such as phosphates, carbonates and silicates, forming lanthanum salts. The bond between lanthanum and ortho-phosphate (LaPO4) is particularly strong and stable under many environmental conditions (solubility product: log(Ksp) ~ -25).
In nature Lanthanum can be found in minerals together with lanthanoids such as Cerium (Ce) and Neodymium (Nd)
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