Vermiculite is a hydrous phyllosilicate mineral which undergoes significant expansion when heated. Exfoliation occurs when the mineral is heated sufficiently, and commercial furnaces can routinely produce this effect. Vermiculite forms by the weathering or hydrothermal alteration of biotite or phlogopite. Large commercial vermiculite mines currently exist in Russia, South Africa, China, and Brazil.
It typically occurs as an alteration product at the contact between felsic and mafic or ultramafic rocks such as pyroxenites and dunites. It also occurs in carbonatites and metamorphosed magnesium-rich limestone. Associated mineral phases include: corundum, apatite, serpentine, and talc. It occurs interlayered with chlorite, biotite and phlogopite.
Calcium silicate boards: exfoliated vermiculite is added to a calcium silicate slurry. This is then dewatered by pressing or by using one of the Fourdriner/Magnani/Hatschek processes to form a flat board which is then heat cured under pressure (typically 10–15 bar) for periods of up to 24 hours.
Brake linings: finer grades of exfoliated vermiculite are being used in brake linings primarily for the automotive market. The properties of vermiculite that make it an appropriate choice for use in brake linings include its thermal resistance, ease of addition to other raw materials to achieve a homogeneous mix, and its shape and surface characteristics.
Storing bulbs and root crops: pour vermiculite around bulbs placed in container. If clumps are dug, allow to dry for a few hours in the sun and then place in cartons or bushel baskets and cover with vermiculite. The absorptive power of vermiculite acts as a regulator that prevents mildew and moisture fluctuation during the storage period. It will not absorb moisture from the inside of stored tubers, but it does take up free water from the outside, preventing storage rot.
As a constituent of a coating: vermiculite dispersions are typically either chemically or physically very finely delaminated vermiculite in a fluid medium. These dispersions can be used to make vermiculite 'paper' sheets by pouring them onto a piece of smooth, low surface-energy plastic, and allowing to dry. The resulting sheet can then be peeled off the plastic. Typical end-uses for vermiculite dispersions include inclusion in high temperature coatings or binders for construction materials, gaskets, specialty papers/textiles, oxidation-resistant coating on carbon based composites, and as barrier coatings for films.
In 2014, South Africa, Brazil, the US, and China were the top producers of mined, concentrated and unexfoliated vermiculite, with about 90% world share. South Africa's production is decreasing, while Brazil's is significantly increasing.
Today spray-applied fireproofing materials use vermiculite, other industrial minerals, and expanded polystyrene, depending upon the exact commercial product. The ingredients for these products all have to meet stringent regulatory requirements, particularly in the US and Europe. In the past, vermiculite from the W. R. Grace mines in Libby, Montana, have been associated with asbestos. Therefore, old spray-applied fireproofing, pre-1991, may contain small quantities of asbestos. In August 2014, the NYSDoH qualified two, more exact, test methods, better designed to identify materials with this potential problem, and assist in safely dealing with any issues associated with its removal. Modern spray applied fireproofing today is made with various light weight aggregates that does not contain asbestos and is carefully monitored at all stages of mining and production to ensure this is the case.