Abstract
Ammonium-bearing dioctahedral mica was found in an argillized vein in the hydrothermally altered andesite from the Aira district, Kagoshima Prefecture. X-ray, thermal and infrared absorption data agree with those of ammonium-bearing micas studied earlier. However the hkl reflections from x-ray analysis and a doublet band due to the Si-O vibration in infrared absorption spectra after heating at 700°C indicate that the specimen belongs to 2M1 polytype. The unit cell parameters are a0=5.16 (2)Å, b0=9.02 (2)Å, c0=20.28 (7)Å and β=96.36°. Chemical analysis of the mineral shows a structural formula of ((NH4) 0.20K0.51Na0.18Ca0.00)(Al1.89Ti0.00Fe3+0.03Mg0.06)(Si3.25Al0.75) O10 (OH) 2, and the specimen is relatively rich in sodium, and has a larger total layer charge than that of ammonium-bearing micas reported so far.
