Studies of mineral surface interactions with water using pycnometric measurements

This paper describes how simple pycnometric studies using water and a non-polar fluid such as n-heptane, may be used to recognise the presence and indicate the magnitude of chemical “reactions” between mineral surfaces and water. The results of such studies on glass, feldspar, quartz, and olivine, are reported, together with observations of the influence changes in pH can have upon such mineral–water responses. In all cases the mass density of these solids was lower when measured in water than that measured in n-heptane, suggesting their contact with water creates a boundary layer of lower density material around the particles; differences of up to 11% are possible. Such boundary layers can influence mechanical properties and could partly explain time dependent behaviour under constant effective stress. They also respond differently to solutions of different pH, with measured density decreasing by approximately 7% as pH increases from 3 (strongly acidic) to 11 (strongly basic). Such phenomena add a new field of studies to the description, investigation and quantification of soils and rocks.