This humble mineral expands like a worm when heated to become a global powerhouse.
In short: Named for the Latin word for breeding worms, vermiculite is a unique clay mineral that undergoes dramatic expansion when heated. From insulating molten steel to helping your garden soil breathe, this versatile material has been a quiet staple of modern industry and horticulture for nearly two centuries.
Vermiculite is a hydrous phyllosilicate mineral, a 2:1 clay formed through the weathering or hydrothermal alteration of biotite or phlogopite. Its defining characteristic is exfoliation: when heated, the mineral expands significantly, a process first described in 1824 after its discovery in Millbury, Massachusetts. Geologically, it typically appears at the contact zones between felsic and mafic rocks, often found alongside minerals like corundum, apatite, and serpentine.
The mineral's utility stems from its high cation-exchange capacity and its ability to retain liquids within its inter-laminar voids. In horticulture, it is prized for creating air channels in heavy soils and holding moisture in sandy ones, a practice pioneered by Boodley and Sheldrake. Beyond the garden, its thermal resistance makes it essential for high-temperature insulation, fireproofing structural steel, and even serving as a blast mitigant in explosives storage. It is also used in automotive brake linings and as a base for swimming pool liners.
Despite its widespread utility, vermiculite has a complicated history regarding safety. While pure vermiculite is non-toxic, some deposits are contaminated with asbestos. The most infamous example is the mine in Libby, Montana, which operated from the 1920s until 1990. Once responsible for an estimated 80% of the world's supply, the Libby mine produced vermiculite contaminated with tremolite, winchite, and richterite. Today, the industry is strictly regulated, and mines are regularly tested to ensure products are asbestos-free.
Global production remains concentrated, with South Africa, Brazil, the United States, and China accounting for about 90% of the world's share as of 2014. Industry interests are represented by The Vermiculite Association, which facilitates information exchange among processors who often blend the mineral with other materials like perlite or cement to meet specific technical requirements for construction and industrial applications.
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Sources
- Summary by Intellect · source: Vermiculite
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