ˈiˌlīt noun
( -s )
Etymology: Ill inois (state) + English -ite
1. : a group of minerals found in clays and having essentially the crystal structure of muscovite
2. : one of the minerals of the illite group ; especially : the mineral having the composition of muscovite or of a hydrated muscovite but giving a line-poor X-ray powder pattern
• il·lit·ic (ˈ)i|lid.ik, -līd.- adjective