The unit cell of NaCaHSiO4: An electron‐microscope and X‐ray study

Results of selected-area electron diffraction show that NaCaHSiO4 is monoclinic, with a = 5.72, b = 7.06, c = 5.48 A, β = 122.5°, Z = 2, space group P21 or P21/m. A larger, B-centred monoclinic unit cell can also be chosen and is dimensionally similar to the orthorhombic cell of Na2SO4(III) to which NaCaHSiO4 may be structurally related. NaCaHSiO4 may also be structurally related to several of the Ca2SiO4 polymorphs. Indexed X-ray powder data are given.