Sunday stone

[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.

[2] In one case, a broad stripe coincided with workers being given the day off to view a cockfight.

[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.