Perlite from the Greek islands of Milos, Kimolos and Kos is compositionally a calc-alkaline rhyolite that consists principally of glass (>85%) with minor amounts of phenocrysts. Different textural types can be recognized with varying degrees of vesicularity, including a classical perlite with spheroidal fractures of 'onion-skin' type.

A wide variety of samples were expanded in a laboratory furnace and the bulk density and other properties relevant to the uses of the expanded material were determined. Only a small amount of non-expanded material remained after heating. The bulk density of the expanded perlite covers a broad range, from 25 to 230 kg/m3, and is partly dependent on the size of the feed. The compaction resistance is variable, but high oil absorption (400-2200 ml/100 g) and specific surface area (6-13 m2/g) are obtained. These properties appear to be independent of the bulk density. It appears that the expansion characteristics are more dependent on furnace conditions than on any minor variations between the perlite types.

Once expanded, the product lends itself to most perlite applications. The coarser expanded material from Milos is best suited for concrete, plaster and horticulture. The lowest-density expanded perlite from all three islands is suitable for loose-fill insulation applications and the finer fractions are appropriate for cryogenic, filter-aid and filler purposes. Kimolos expanded perlite is probably best suited for the animal feed and thermal insulation markets.