Vermiculite.  Ontario.

Vermiculite. Ontario.

Vermiculite is a hydrous phylosilicate mineral, (Mg,Fe2+, Fe3+ )3(Al,Si)4O10 (OH)2 . 4H2O  This clay mineral has the property of  expansion to 8 to 20 times of its original size when heated, which makes it very useful in cement, and insulation products. It is also widely used as a soil additive in gardening products. This particular specimen is from Ontario, Canada.