"The washability characteristics of a coal reserve are provided by obtaining liberation data on the raw coal. Liberation refers to the amount of physical breakage required to separate material of different material densities. Low density material is clean coal whereas high density material is reject (rock). The intermediate density material is called middlings." --(http://en.wikipedia.org/wiki/Coal_washing)
Synonyms: unexceptional, mediocre, average, run-of-the-mill, common
Antonyms: exceptional, extraordinary
"Overburden is the material that lies above an area of economic or scientific interest in mining and archaeology; most commonly the rock, soil and ecosystem that lies above a coal seam or ore body. It is also known as 'waste' or 'spoil'. Overburden is distinct from tailings, the material that remains after economically valuable components have been extracted from the generally finely milled ore. Overburden is removed during surface mining, but is typically not contaminated with toxic components and may be used to restore an exhausted mining site to a semblance of its appearance before mining began. Overburden may also be used as a term to describe all soil and ancillary material above the bedrock horizon in a given area.
A related term is interburden, meaning material that lies between two areas of economic interest, such as the material separating coal seams within strata.
By analogy, overburden is also used to describe the soil and other material that lies above a specific geologic feature, such as a buried astrobleme." --http://en.wikipedia.org/wiki/Overburden
"Overburden,‥a term used by geologists and engineers in several different senses. By some it is used to designate material of any nature, consolidated or unconsolidated, that overlies a deposit of useful materials, ores, or coal, especially those deposits that are mined from the surface by open cuts. As employed by others overburden designates only loose soil, sand, gravel, etc., that lies above the bedrock." --OED
Civil Engineering sense: " A more detailed soil investigation of the upper 50 ft or so of the overburden‥showed that the allowable bearing capacity was only about 200 to 300 psf, much too low for the proposed bridge foundations." --OED
["The bridge gathers to itself in its own way earth and sky, divinity and mortals" --Heidegger, "Building, Dwelling, Thinking
"Thus the bridge does not first come to a location and stand in it; rather, a location comes into existence only by virtue of the bridge" --Heidegger, "Building, Dwelling, Thinking" ]