The name Vermiculite derives from the latin word “vermiculari” which means ‘to produce worms’ and was coined by Mr. T. H. Webb, for the first time in 1824, in Milbury, Worcester (MA), in reference to the reaction of this mineral in the presence of a flame. Other terms such as ‘Happy Mica’, ‘Gold Mica’, ‘Gold Feather’ or ‘Mineral Cork’ were also applied but are no longer in use.
Today Vermiculite is the mineralogical term used to describe the industrial and commercial group of minerals having a lamellar structure and which belongs to the mica family. According to ‘Gruner’ who first studied Vermiculite in 1934 the crystalline mesh has the aspect of ‘biotite’ in which numerous water molecules are present. Chemically speaking Vermiculite is an Aluminium Silicate and Hydrated Manganese with a rough formulation given as:
22Mg • 5Al2O3 • Fe2O3 • 22SiO2 • 40H2O
In practical terms, the centesimal chemical analysis of typical vermiculite ores not only has always shown the presence of Mg and Al, but also of other Cations (Na, K, Ti, Mn, Ca). The quantity of these Cations is always modest and therefore they are regarded as impurities and not shown in the final chemical formulation.
Generally, Vermiculite is found to be mixed-in with other minerals such as (talc), asbestos, corundum apatite, chlorite and biotite. Depending on the ore source Vermiculite will come in a number of colours. They can vary from black, to yellow, through a number of dark tints.
Vermiculite is insoluble in water and neutral. However depending on the ore source, the pH can vary from 6 (slightly acidic) to 7.8 (slightly caustic).
Vermiculite can be dissolved by strong acids and is not modified by strong basic elements. It works well mixed in with cement and lime and remains unadulterated after mixing.
It is well know that the most important parameters related to the assessment of the viability of a particular Vermiculite ore is not a direct chemical analysis but rather the water of crystallisation which in the case of really good vermiculite should not be below 5%.
Most vermiculite ores are used only after exfoliation.