Calorimetric measurements were made of the heat of immersion in water of cassiterite that was either untreated or treated
with 60% HNO3. The heats of immersion of cassiterite and fluorite were also calculated theoretically from the surface Gibbs energy components,
and compared with the heat of immersion measured for cassiterite and that taken from the literature for fluorite. The results
of the measurements and calculation revealed that the heat of immersion depends on the degree of hydration of the surface
of cassiterite and fluorite. It was also found that it is possible to predict the heats of immersion in water of cassiterite
and fluorite from the Lifshitz-van der Waals and acid-base components of the surface Gibbs energy.