A new layered silicate (denoted as FLS1) has been prepared from reaction of H-magadiite in tetramethylammonium hydroxide (TMAOH) and water via hydrothermal treatment for 5 days at temperatures higher than 150 degreesC. When the product is heated to 500 degreesC, the layered silicate is converted to a three-dimensional network through condensation of hydroxyl groups and cross-linking of the layers. The calcined phase is stable up to 900 degreesC and has a surface area of 437 m(2) g(-1), more than 10 times larger than that of the starting H-magadiite (40 m(2) g(-1)). The external surface area and micropore volumes were determined using a new method, similar to that reported previously for pillared materials. The micropore volume of FLS1 calcined at 500 degreesC is about 0.130 mL (liquid nitrogen) g(-1). The solid-state transformation of FLS1 into a TMA-containing sodalite structure in a sodium aluminate and TMAOH(.)5H(2)O mixture at 150 degreesC for 2 h is also reported.