Here's why:

* Clay particles are very small. They are less than 0.002 mm in diameter, making them practically invisible to the naked eye.

* Clay particles are tightly packed. This tight packing gives clay soil its characteristic solidity.

* Clay has a high water holding capacity. This is due to the small particle size and the presence of many tiny spaces between the particles.

While clay can become soft and malleable when wet, it dries to a hard, solid state.