Which mineral is NOT a phyllosilicate?

• A. Kaolinite
• B. Muscovite
• C. Chlorite
• D. Quartz

Answer: (D)

Sheet silicates, or phyllosilicates, are built from silicate tetrahedra arranged in planar sheets with relatively weak bonding between those sheets. This structure gives characteristic sheet-like cleavage and specific layering in the minerals.

Kaolinite, muscovite, and chlorite all have this sheet architecture: their crystal structures are formed from tetrahedral sheets linked into layers, with other cations or hydroxide layers between the sheets. Quartz, however, does not have sheets. It forms a three-dimensional framework where every silicon tetrahedron shares all four oxygen corners with neighbors, creating a sturdy network without sheet layers. This framework silicate explains quartz’s lack of sheet cleavage and its high hardness.

So the mineral that is not a phyllosilicate is quartz.