Silicon isotope ratios ( 28 Si, 29 Si and 30 Si) can be measured with high precision by multi-collector inductively coupled plasma mass spectrometers (MC-ICP-MS). However, the problematic extraction of silicon from geological materials has been a major disadvantage in previous silicon isotope studies with conventional gas source mass spectrometry, whereas available silicon isotope results obtained by MC-ICP-MS techniques have been mainly restricted to waters and high purity silica. We show here that high yields of silicon (>97%) can be achieved from samples ranging from pure silica to basaltic compositions (45-52 wt.% SiO 2 ) via a three-step digestion and purification procedure. Silicon isotope measurements, performed with a Finnigan Neptune MC-ICP-MS used in medium-resolution mode (resolving power: 2500), indicate that polyatomic interferences can be resolved and that both d 29 Si and d 30 Si can be determined with high accuracy and precision on interference-free peak plateaux in the mass spectrum. Instrumental blanks (20-65 mV) were reduced to acceptable values with a Cetac Aridus desolvating device fitted with a sapphire injector in the torch. Sensitivity in medium-resolution mode is in the range of B6 V per mg g À1 for 28 Si. d 29 Si and d 30 Si have been determined for silicon isotope standards IRMM-018 (d 30 Si = À1.75%), IRMM-018-76 (d 30 Si = À1.42%), Diatomite (d 30 Si = 1.34%) and Big Batch (d 30 Si = À10.52%), for USGS standards BHVO-2 (d 30 Si = À0.09%) and AGV-2 (d 30 Si = À0.01%), and for Aldrich pure silica powder (d 30 Si = À0.32%). Precision on d 30 Si is 0.18-0.41% (2 s.d.). Our combined procedure for sample preparation followed by high-resolution MC-ICP-MS analysis facilitates straightforward and safe measurement of silicon isotope ratios in silicate materials.