Perlite

Perlite forms when obsidian, a silica-rich volcanic glass, undergoes hydration over geological time, incorporating 2–5% water by weight. This water is held in the glass structure and is the key to its expansion. When heated rapidly to 850–1100°C, the water vaporizes, creating countless tiny bubbles that expand the material 4 to 20 times its original volume¹. The resulting expanded perlite is white, porous, and extremely lightweight, with a bulk density of 50–200 kg/m³ and low thermal conductivity.

Expanded perlite is widely used as an aggregate in lightweight plasters, concrete, and roof insulation boards, and as a loose-fill insulation in walls and attics. Its fire resistance (melting point above 1200°C) and acoustic properties make it valuable in building materials. In horticulture, it improves aeration and drainage in potting mixes and hydroponic systems. Industrial applications include filter aids for food and beverage processing, cryogenic insulation for LNG storage, and as an abrasive or filler in various products².

Perlite is mined in over 30 countries, with China, Turkey, Greece, and the United States leading production. In 2023, global production was estimated at 5.4 million tonnes, with the U.S. producing about 800,000 tonnes. The ore is crushed, dried, and graded before being expanded in vertical furnaces. The expansion process is energy-intensive, and the industry has focused on optimizing furnace design and reducing emissions. The market is projected to grow due to demand in construction and agriculture, particularly in developing regions.

Perlite has several niche applications: it is used as a lightweight aggregate in geopolymer concrete, a carrier for herbicides and fertilizers, and a medium for cryopreservation of biological samples. In the 1940s, perlite was used as a substitute for sand in sandblasting. A notable historical use was in the construction of the 1962 Seattle Space Needle, where perlite was used in the concrete to reduce weight³. Perlite is also used in the restoration of historic buildings due to its compatibility with lime plasters. Additionally, expanded perlite is used as a filter medium in swimming pools and as a soil amendment in viticulture to improve water retention in sandy soils.

Obsidian

A naturally occurring volcanic glass formed from felsic lava, which hydrates to form perlite.

Expanded perlite

The product of heating perlite ore to high temperatures, causing it to expand into a lightweight, porous material.

Bulk density

The mass per unit volume of a powder or granular material, including the voids between particles.