Vermiculite

Vermiculite is a natural mineral that expands with the application of heat. The expansion process is called exfoliation and it is routinely accomplished in purpose-designed commercial furnaces. Vermiculite is formed by hydration of certain basaltic minerals. The former W.R. Grace mine in Libby, Montana was the largest and oldest vermiculite mine in the United States, but other deposits exist in South Carolina and Virginia, and large commercial vermiculite mines currently exist in South Africa, China, Brazil, and several other countries.

Structure

Vermiculite is a 2:1 clay, meaning it has 2 tetrahedral sheets for every one octahedral sheet. It is a limited expansion clay with a medium shrink-swell capacity. Vermiculite has a high cation exchange capacity at 100-150 meq/100g. Vermiculite clays are weathered micas in which the K⁺ ions between the molecular sheets are replaced by Mg²⁺ and Fe²⁺ cations.

Commercial uses

• moulded shapes, bonded with sodium silicate for use in:
  • high-temperature insulation
  • refractory insulation
  • fireproofing of structural steel and pipes
• soil conditioner
• as loose-fill insulation
• packing material, valued for its high absorbancy
• suitable as a substrate for various animals and/or incubation of eggs
• lightweight aggregate for plaster, proprietary concrete compounds, firestop mortar and cementitious spray fireproofing
• component of the interior fill for firestop pillows, along with graphite
• carrier for dry handling and slow release of agricultural chemicals
• soil additive for plants, together with perlite for potted plants
• growing medium for hydroponics.
• means to permit slow cooling of hot pieces in glassblowing, lampwork, steelwork, and Glass beadmaking
• used in in-ground swimming pools to provide a smooth pool base
• used in commercial handwarmers