Electron microscope study of the humite minerals: I. Mg-Rich specimens

Natural humite minerals and synthetic fluoro-humites, ideally described as nMg₂SiO₄ · Mg(OH,F)₂ (1<n<4), were investigated by using electron diffraction and imaging techniques. In clinohumite (n=4) and humite (n=3) irregularities in lattice spacings were observed parallel to (001). These were identified, using high resolution lattice images, as upper member lamellae in which n was always even (i.e., n=6, 8, 10 etc.). In fluoroclinohumite the higher members were sometimes perfectly ordered, giving rise to superstructures with relatively large c axes. These supercells always consisted of several consecutive unit cells of clinohumite (n=4) followed by a unit cell of the n=6 member; the largest observed had a d (001) spacing of 169 Å. It was also found that coherent intergrowths of massive portions of humite (n=3) and chondrodite (n=2) often occurred.