Table 1. Main data for the studied samples, including labels, location and mineralogical compositions (from XRD data) of impurities that appear with the smectite.

The order of impurities is related to their abundance, starting with the most abundant. Minerals in parentheses are ≤5% in weight, and minerals indicated with an asterisk (*) are present at trace level.

Quarry (location)	Label	Impurities
Cortijo de Archidona (Cabo de Gata, Spain)	CAR1	(Quartz)
	CAR2	(Plagioclase, Quartz)
Los Trancos (Cabo de Gata, Spain)	LTBB	(Quartz, Plagioclase*)
Crook County (Wyoming, USA)	WYO	Quartz, (Illite)
Esquivias (Tajo Basin, Spain)	ESB6	Illite, (Quartz, Kaolinite, Feldspar)
Magán Hill (Tajo Basin, Spain)	RESQ	Calcite*
	ROS	Calcite*