Information on the nature, physicochemical properties, and environmental fate of nanoparticles is severely lacking. Zeolite A was used to demonstrate its structural transformation from well crystalline to short‐range‐ordered (SRO) particles, including nanoparticles with size fractions in the range of 450 to 2000, 100 to 450, 25 to 100, and 1 to 25 nm. The chemical properties of a zeolite are dependent on its framework structure, which is formed by connecting truncated octahedra (sodalite) through the simple double four rings (D4‐R) with external linkage in each sodalite. With decreasing particle size, the T(Si, Al)‐O asymmetric and symmetric stretching vibrations shifted toward higher frequencies and the Si to Al molar ratio increased consistently from 1.8 to 5.2. The chemical shift of 27Al and 29Si magic‐angle spinning (MAS) nuclear magnetic resonance (NMR) spectra was related to its structural transformation from well crystalline to SRO particles, which was attributed to the loss of external linkage D4‐R units in the structure. Comparing the various particle‐size fractions (PSFs) showed significant differences in surface area, Si/Al molar ratio, morphology, crystallinity, framework structure, and surface atomic structure of nanoparticles from those of the bulk sample (i.e.,<2000 nm) before particle‐size fractionations. Formation of these most reactive nanoparticles were caused by physicochemical weathering merits increasing attention with reference to their nature and properties, and their importance in ecosystem integrity.