The Old Mine diamond obtained its name from the fact that the greater percentages of these cushion shaped, fine old mine, diamonds were hand facetted at the site where the rough octahedral diamond crystals were found.
The naturally formed, four sides of the crystal had each of the four corners rounded off by the cutter creating a cushion shaped, “old mine diamond” which was then fashioned AT the mine site. One end of the crystal was then laboriously ground down to form a flattened table facet. The remaining 50 plus faces were added and finally the bottom pointed area of the diamond was flattened off to a small flat facet called a culet.
Many of the old mine diamonds came from the Cape of South Africa’s famed diamond fields and had a 
proliferation of nitrogen in their crystal lattice work. This proclivity towards nitrogen frequently caused the yellowish tinge in these diamonds and thus the term “Cape Diamond” was coined since most of these diamonds demonstrated this characteristic. The proliferation of nitrogen in many of these older diamonds cause them to “fluoresce” a slight to strong, vivid blue colouration thus “improving” the apparent body color of the diamond. This trait is particularly difficult to detect in many diamonds set in pieces of jewelry where these old mine diamonds are found.