"Sunday stone" is an artificial stone composed of calcium carbonate that formed on the walls of drainage pipes in some coal mines. [1] [2] It is striped due to the differing levels of coal dust produced during the day and night shifts. [1] In some cases, a broader stripe is generated every seven days due to active mining not taking place on Sunday. [1] Broader stripes would also appear when work stopped for other reasons. [2] In one case, a broad stripe coincided with workers being given the day off to view a cockfight. [2] Breaks of more than a day would produce an even broader stripe, such as when Christmas fell on a Monday. [2]
The Sunday stone would over time block the drainage pipes necessitating their replacement. [1] Where mines have improved ventilation, reducing the level of coal dust in the air, Sunday stone has ceased to be formed. [1]