A mild acid attack of the Llano vermiculite produces porous materials suitable for use as cracking catalysts and/or catalysts supports. After HCl attack at 80°C (1 m), the number of acid sites measured by the Hammett indicator method is ∼0·50/nm2, and the specific surfaces are 245 m2/g after calcination at 550°C (4 h), and 55 m2/g after steaming at 750°C (4 h). The performance of leached (1 m HCl) vermiculite has been compared with another hydrocarbon cracking catalyst—γ-Al2O3. The leached vermiculite produces a definite higher conversion and higher C3, C4 and gasoline yields, but much lower coke production. By electron microscopy, infrared spectroscopy, X-ray powder diffraction and thermal analysis, it has been shown that the leached vermiculite samples are composed of more or less attacked layers retaining their original platy morphology, and non-crystalline hydrated silica. Chemical analyses indicate that octahedral cations are dissolved first.