subject: Vermiculite - A Resourceful Mineral [print this page] Vermiculite was first depicted at Millbury, Massachusetts, USA in 1824. Vermiculite is a mineral that belongs to phyllosilicate group of minerals which is similar to mica in appearance. The mica includes Biotite, Muscovite, Lepidolite and Phlogopite. Thus Vermiculite is formed by weathering of Biotite and Phlogopite minerals. It is basically known as hydrated phlogopite mica which has the significant capacity to expand.
The mineral has deposits of water sandwiched between the layers of silicate, like other mineral talcs. When the mineral imposed to heat, water dries away and it exfoliates or expands far and wide. Thus by this property of expansion, the mineral forms a worm like structure. The term vermiculite is derived from a Latin word vermiculare which means worm-like. The significant factor is that the mineral expands to several times its original volume. By so many experiments, it is found that it expands 10 times more than its original volume, hence referred as quality rich mineral. If the mineral expands less than 10 times of its original volume, then it is referred as low grade.
The basic structure of Vermiculite is identical to mica sand to talc. The silicate sheet is formed in the 2:1 ratio which means two parts of tetrahedral sheets for every one octahedral sheet. Thus the flat layers of silica and alumina tetrahedral layers are combined together with the composed layer of apical oxygen atoms, iron, magnesium and hydroxyl molecules which is octahedral layer. There lies the ion exchangeable layer between these 2:1 layers. The mineral has a high cation exchange capacity at 100-150 meq/100 g. Thus the ion exchangeable layer changes its thickness based on the interlayer cation and the arrangement of water molecules for hydration related with it. Vermiculite clays are also known as weathered micas in which the potassium ions between the molecular sheets are swapped by magnesium and iron ions.
The mineral is generally used as a modification product between felsic and mafic or ultramafic rocks such as pyroxenites and dunites. It is also seen in carbonates and metamorphosed magnesium rich limestone. Some of the associated mineral phases include corundum, apatite, serpentine and talc.
When excavated, the vermiculite is in the form of crumbles or flakes made up of several thin layers. Thus when it is exposed to high temperature, water gets dried up and the steam produced spreads all over the layers, causing the flakes to exfoliate as much as 10 to 20times its original size. The fine particles of the mineral can absorb up to 500 times its weight in water.
Vermiculite is widely used in its exfoliated form, mainly in construction and agriculture. Few are used as fillers in paint, plastics and rubber. In construction, vermiculite replaces sand. It also serves as excellent fireproof concretes and plasters. The concrete cannot support heavy weight, but its properties make it useful for roof decks, partitions, prefabricated panels, and firewalls. Vermiculite plaster is mainly used for fireproofing. Vermiculite is a good absorbent that it prevents the soil from crusting and insulates the soil from varying temperature and pressure.
