2. Nature and physico-chemical characteristics

2.1 Nature of the shale

Shale can vary considerably in composition, depending on geographical location and mining basin.

For the Nord-Pas-de-Calais coal mines :

• 20 to 50% sandstone ;

• 50-80% schist from metamorphosed clays;

• 0 to 20% more or less carbonaceous elements.

Spoil heaps still rich in fuel were washed to extract it and direct it to thermoelectric power stations.

• Constituents of black and orange shale : $\text{quartz}-\text{feldspaths}-\text{mica}-\text{argiles}-\text{oxydes}\text{de}\text{fer}$

...