2 : 1 : 1 type of clay mineral contain and extra sheet of . . . . . . . . as compared to 2 : 1 type of clay minerals

Solution (By Examveda Team)

2 : 1 : 1 type of clay mineral contains an extra sheet of Brucite as compared to the 2 : 1 type of clay minerals.
Brucite is the mineral form of magnesium hydroxide and is a common alteration product of periclase in marble. It adopts a layered Cdl₂- like structure with hydrogen bonds between the layers.