C-axis spacing of illite is

IIIite is a group of closely related non-expanding clay minerals. It is a secondary mineral precipitate and its structure is a 2 : 1 sandwich of silica tetrahedron-alumina octahedron-silica tetrahedron layers. C-axis spacing of illite is $${\bf{100 \,nm \,or\, 10}}\mathop {\bf{\,A}}\limits^{\bf{O}} {\bf{.}}$$