Trace element
In analytical chemistry
Analytical chemistry
Analytical chemistry is the study of the separation, identification, and quantification of the chemical components of natural and artificial materials. Qualitative analysis gives an indication of the identity of the chemical species in the sample and quantitative analysis determines the amount of...

, a trace element is an element
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...

 in a sample that has an average concentration
In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration...

 of less than 100 parts per million measured in atomic count, or less than 100 micrograms per gram.

In biochemistry
Biochemistry, sometimes called biological chemistry, is the study of chemical processes in living organisms, including, but not limited to, living matter. Biochemistry governs all living organisms and living processes...

, a trace element is a dietary mineral
Dietary mineral
Dietary minerals are the chemical elements required by living organisms, other than the four elements carbon, hydrogen, nitrogen, and oxygen present in common organic molecules. Examples of mineral elements include calcium, magnesium, potassium, sodium, zinc, and iodine...

 that is needed in very minute quantities for the proper growth, development, and physiology of the organism.

In geochemistry
The field of geochemistry involves study of the chemical composition of the Earth and other planets, chemical processes and reactions that govern the composition of rocks, water, and soils, and the cycles of matter and energy that transport the Earth's chemical components in time and space, and...

, a trace element is a chemical element whose concentration is less than 1000 ppm or 0.1% of a rock
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...

's composition. The term is used mainly in igneous petrology
Igneous petrology
Igneous petrology is the study of igneous rock, those that are formed from magma. Igneous petrology is as a branch of geology closely related to volcanology, tectonophysics and petrology in general. The modern study of igneous rocks is done using several techniques some of the developed in the...

. Trace elements will either prefer liquid or solid phase. If compatible with a mineral, it will prefer a solid phase (E.G. Ni compatible with Olivine). If it is incompatible with an element it will prefer a liquid phase. The measurement of this ratio is known as the partition coefficient. Trace elements can be substitutes for network-forming cations in mineral structures. Minerals do not have to contain trace elements I.e they do not have to appear in in the mineral's chemical formula.
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