Novel layered silicates (denoted as alpha-HLS, alpha-HLS-AN1, gamma-HLS) have been synthesized by hydrothermal treatment from SiO2, tetramethylammonium hydroxide, NaOH, and 1,4-dioxane. The effect of the NaOH concentration and reaction time was investigated. With increasing the concentration of NaOH, the obtained silicate was changed from alpha-HLS to beta-HLS, which was previously reported as HLS (helix layered silicate). X-ray diffraction patterns of alpha- and beta-HLS were very close to each other but there was some differences in their structure and in the temperature stability. (C) 2004 Elsevier B.V. All rights reserved.