Crude vermiculite from the mine consists of golden / brown / silver, flakes which are carefully classified into five grades – each having a specified range of particle sizes. The coarsest grade comprises particles ranging between 1mm and 7mm, while the finest grade consists of particles between 0.710mm and 0.250mm in size. The loose bulk density of crude Vermiculite varies with the grade, but is typically between 700 and 1050 kg/m3.
The exfoliation process is carried out commercially by passing crude vermiculite through a furnace chamber in a controlled manner. The crude vermiculite then expands at right angles to the cleavage planes, producing concertina-shaped particles many times their original volume.
Why does vermiculite exfoliate?
The interlayer water is an essential component in the vermiculite. When a particle of vermiculite is rapidly heated, the interlayer crystalline water transforms into steam. The pressure of this steam evolution, forces the silicate layers apart from one another and the vermiculite flake forms an elongate concertina like particle twenty to thirty times its original thickness.