Today scientists say that all the chemical elements known to nature can be detected in any mineral sample. All without exception. Of course their proportion varies immensely.

   But why is there so much of some and so little of others?

  In the Periodic System all the elements have equal rights. Each occupies its own definite place. But when it comes to the terrestrial reserves of the element, these equal rights vanish into thin air.

   The light elements of the Mendeleyev Table, its first thirty or so representatives, at any rate, constitute the bulk of the Earth's crust. But there is no equality among them either. Some are more abundant, others less. For instance, boron, beryllium and scandium are among the very rare elements.

   Since the Earth has been in existence there has been something of a "revision" of the supplies of its elements. A considerable amount of uranium and thorium has disappeared owing to their radioactivity. A large amount of the noble gases and hydrogen has been lost to outer space. But the general picture has not changed.

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