放射性元素的分布合理的分类方法必须考虑Th,U,K元素在火成岩和沉积岩中的分布。在这三种天然放射性元素中含量最高的是K,它主要赋存在碱性长石、云母、石榴石和霞石中。在石英、长石这些主矿物中只有微量的U和Th;但在锆石、独居石、磷钆矿等副矿物的细小晶粒中,U和Th的含量却要高得多。通常,含有大量U和Th的多数矿物是火成岩结晶过程的后期形成的。U,Th和K通常具有相似的地球化学特性。U和Th均为钢系元素,并在化学还原条件下都是四价态;而在氧化条件下U为 Distribution of radioactive elements A reasonable classification method must consider the distribution of Th, U, K elements in igneous rocks and sedimentary rocks. The highest content of these three natural radioactive elements is K, which is mainly found in alkaline feldspar, mica, garnet and nepheline. In quartz and feldspar, these minerals are trace amounts of U and Th; however, the contents of U and Th are much higher in fine grains of accessory minerals such as zircon, monazite, and gadolinite. In general, most minerals that contain large amounts of U and Th are formed later in the igneous crystallization process. U, Th and K usually have similar geochemical characteristics. U and Th are steel elements, and in the chemical reduction conditions are tetravalent state; while in the oxidation conditions U