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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%).
Heavy metals is a controversial and ambiguous term [2] for metallic elements with relatively high densities, atomic weights, or atomic numbers. The criteria used, and whether metalloids are included, vary depending on the author and context and has been argued should not be used.
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The table is color-coded to show the chemical groupings. Small symbols pack in additional information: solid/liquid/gas, the color of an element, common in the human body, common in the earth's crust, magnetic metals, noble metals, radioactive, and rare or never found in nature.
Regardless of significant differences between abundances of several elements in urban soils and those values calculated for the Earth's crust, the element abundances in urban soils generally reflect those in the Earth's crust. With the development of technology the abundances may be refined. Mass fraction, in mg/kg (ppm).
The abundance of the chemical elements is a measure of the occurrences of the chemical elements relative to all other elements in a given environment. Abundance is measured in one of three ways: by mass fraction (in commercial contexts often called weight fraction), by mole fraction (fraction of atoms by numerical count, or sometimes fraction of molecules in gases), or by volume fraction.
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"The earth's crust" in Clarke and Washington works can mean two different things: (a) The whole outer part of Earth, i.e. lithosphere, hydrosphere and atmosphere; (b) Only the lithosphere, which in their works just meant "the rocky crust of the earth". "Crust" here means (b). Following tables do not cover all elements.