A highly crystalline ZSM-5 product was obtained from diatomite, a natural raw material, both with and without the presence of diethanolamine. The synthesis process took 40 h, and was carried out under hydrothermal conditions, at autogenic pressure, and at a temperature of 180 degreesC. The resulting crystals were identified as ZSM-5 by X-ray diffraction and characterized by scanning electron microscopy, infrared spectroscopy, thermal gravimetry and differential thermal analysis. (C) 2004 Society of Chemical Industry.