In clay science, micropores (Figure 3) are cavities with diameters of <2 nm within a sample, following the IUPAC convention (Rouquerol et al., 1996), which is also similar in size to a common (upper) clay particle size used in clay studies. Thus, these pores are probably present at the edges of single stacks of unit structures and at widened edges of the interlayer. In soil science, micropores are defined as 5 - 30 μm, ultramicropores are 0.1 – 5 μm, and cryptopores are <0.1 μm (Soil Science Society of America, 1997). The pore volume distribution of clays is commonly determined by gas adsorption methods (typically H₂O, N₂ or, CO₂).
Cf., macropore, mesopore