Perlite is a hydrous form of obsidian, a silica rich volcanic glass formed during the rapid cooling of lava.1 This fast hardening process preserves water (2-5%) inside the aluminosilicate matrix. At temperatures above 800 oC the water encapsulated within the inner layers evaporates causing the perlite grains to expand. The product is a low-density foamed material which has up to 20 times greater volume in comparison to the original material. This research is originally inspired by a quest for fundamental understanding of the perlite expansion process. Industrial grade perlite and expanded perlite systems were studied in detail using solid-state nuclear magnetic resonance (SSNMR) spectroscopy. The SSNMR studies are based on the 1H, 29Si, 27Al single pulse excitation (SPE), 1H-29Si cross-polarization (CP), 27Al Triple Quantum Magic-Angle-Spinning (3QMAS) experiments and the peak simulations. The resonances at ~52 ppm detected in the 27Al MAS SPE spectra are assigned to tetrahedally coordinated aluminium, while the resonance at ~5 ppm, which is only detected in the perlite spectrum, is attributed to octahedrally coordinated aluminium.2 Deconvolution of 27Al MAS SPE spectra obtained at 7.04 and 11.74 T and the 3QMAS experiments do not indicate the presence of pentahedrally coordinated aluminiums. 27Al data implies that tetrahedrally coordinated aluminiums do not participate significantly in the grain expansion process. The broad 29Si MAS SPE peaks of both perlite samples are deconvoluted into four individual resonances which revealed four different Qn configurations for the perlite structure. 1H-29Si CP MAS spectra support the hypothesis about the presence of Q2 units. SEM micrographs revealed the disordered morphology of expanded domains in perlite after heat treatment. FTIR peaks are deconvoluted and Qn units are proposed and compared to those obtained in SSNMR suggesting the prevalence of a Q3 configuration. A plausible mechanism describing structural changes during the heat treatment of perlite is proposed.