Hilt's law is a
geological
Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Eart ...
law that states the deeper the
coal
Coal is a combustible black or brownish-black sedimentary rock, formed as stratum, rock strata called coal seams. Coal is mostly carbon with variable amounts of other Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen ...
, the higher its
rank (grade). The law holds true if the
thermal gradient is entirely vertical, but
metamorphism
Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of ...
may cause lateral changes of rank, irrespective of depth. Increasing depth of burial results in a decrease in the
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as we ...
content of the coals. The phenomenon was observed by professor Carl Hilt (1873).
See also
*
Coal assay
References
* ''Coal Geology by Larry Thomas'',
# , #
Coal
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