Abundance of elements in Earth's crust

The abundance of elements in Earth's crust is shown in tabulated form with the estimated crustal abundance for each chemical element shown as mg/kg, or parts per million (ppm) by mass (10,000 ppm = 1%).

Reservoirs
The Earth's crust is one "reservoir" for measurements of abundance. A reservoir is any large body to be studied as unit, like the ocean, atmosphere, mantle or crust. Different reservoirs may have different relative amounts of each element due to different chemical or mechanical processes involved in the creation of the reservoir.

Difficulties in measurement
Estimates of elemental abundance are difficult because (a) the composition of the upper and lower crust are quite different, and (b) the composition of the continental crust can vary drastically by locality. The composition of the Earth changed after its formation due to loss of volatile compounds, melting and recrystalization, selective loss of some elements to the deep interior, and erosion by water. The lanthanides are especially difficult to measure accurately.

Graphs of abundance vs atomic number
Graphs of abundance against atomic number can reveal patterns relating abundance to stellar nucleosynthesis and geochemistry. The alternation of abundance between even and odd atomic number is known as the Oddo–Harkins rule. The rarest elements in the crust are not the heaviest, but are rather the siderophile elements (iron-loving) in the Goldschmidt classification of elements. These have been depleted by being relocated deeper into the Earth's core; their abundance in meteoroids is higher. Tellurium and selenium are concentrated as sulfides in the core and have also been depleted by preaccretional sorting in the nebula that caused them to form volatile hydrogen selenide and hydrogen telluride.

List of abundance by element
This table gives the estimated abundance in parts per million by mass of elements in the continental crust; values of the less abundant elements may vary with location by several orders of magnitude.