Natural Mica Vermiculite Mineral | eBay | !Rare! Natural Vermiculite mineral from Russia, the Murmansk region, the city of Kovdor, the largest deposit of vermiculite in the world! Weight - 1 kg, 10*6 cm. Vermiculite is a hydrous phyllosilicate mineral. It undergoes a significant expansion when heated. Exfoliation occurs when the mineral is heated, and the effect is routinely produced in commercial furnaces. Vermiculite is formed by weathering or hydrothermal alteration of biotite or phlogopite..