Vermiculite is a member of the phyllosilicate group of minerals, resembling mica in appearance. Palabora vermiculite is essentially a hydrated phlogopite mica, which has the remarkable ability to expand to many times its original volume when heated, a property known as exfoliation.
Crude vermiculite from the Palabora mine consists of golden brown flakes, which are carefully classified into five grades, each having a specified range of particle sizes. The coarsest grade comprises particles ranging between 8mm and 2.8mm, while the finest grade consists of particles between 0.710mm and 0.250mm in size.
Vermiculite is mined from a separate pit, located adjacent to the copper pit. The mining operation involves blasting the ore in the pit, which is approximately 50 metres deep, loading the ore onto trucks, and transporting it to the surface, where it is then sent to the nearby Vermiculite Plant. The pit is a lot shallower than the open copper pit.
At the Vermiculite Plant, the ore is crushed in a single jaw crusher, screened, stockpiled and dried. The drying process takes place in three hot air rotary driers. Once dried, the vermiculite is passed down a series of screens and winnowers where cross current air streams remove the light vermiculite flakes from the heavier particles. This classifying process produces vermiculite flake into seven commercial grades.
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.