Tungusite: new data, relationship and structural model

New chemical analyses, electron and X-ray powder diffraction data, and comparison with gyrolite and reyerite shows the ideal formula for tungusite. A structural model for tungusite is derived by splitting the double tetrahedral layer of reyerite and inserting a trioctahedral X sheet which is ideally occupied by Fe2+. Polytypism phenomena due to different relative positions between tetrahedral and X sheets are discussed. A substitutional solid solution includes tungusite (x = y = z = 0, M = Fe2+) and gyrolite (x = 1, y = 1, z = 6, M = Ca). -from Authors