The facts
What perlite actually is
Mineralogically, perlite is a hydrated volcanic glass containing 2-5% combined water, which expands into a lightweight froth when heated rapidly to 850-900 C — Rhyolitic glass, SiO2 70-75%, with 2-5% H2O, crystallising in the amorphous system.
The colour is caused by grey to greenish glass before expansion; brilliant white after, from light scattering at the cell walls. That is worth knowing because it determines what heating, light and time can and cannot do to the stone.
A refractometer reads 1.48-1.50, and the specific gravity sits near 2.2-2.4 unexpanded; 0.03-0.15 bulk density expanded; cleavage is none; perlitic onion-skin fracture is diagnostic in the raw rock.
Where perlite comes from
The recognised sources are Milos and Kos, Cyclades, Greece - the largest world producer, Izmir, Erzurum and Nevsehir, Turkiye, No Agua and Socorro County, New Mexico, USA and Armenia, Hungary and Iran.
Origin affects price in this material, so we name the locality on every quote rather than the country. "African" or "Asian" tells a buyer nothing.
How perlite is treated
Crushed, graded and expanded in a vertical furnace. Uses: horticultural growing medium and soil conditioner, filter aid for beer, wine, juice and pharmaceuticals, lightweight plaster and concrete aggregate, cryogenic and building insulation, and as an abrasive filler. HEALTH: expanded perlite is amorphous and low in crystalline silica, which is its advantage over diatomite filter aids - but the crushing and expansion dust still requires nuisance-dust control, and some perlite ores contain minor cristobalite.
None of this is a problem when it is said out loud. It becomes one the moment it is left out.
What perlite is confused with
The usual confusions are Diatomite (the competing filter aid, with cristobalite risk), Vermiculite, Pumice (naturally expanded, no furnace needed) and Expanded clay aggregate.
The separation is rarely a matter of opinion: refractive index 1.48-1.50 and specific gravity 2.2-2.4 unexpanded; 0.03-0.15 bulk density expanded settle most of it in a minute, and magnification settles the rest.
What perlite is used for
Perlite is bought by heavy industry, filtration, architecture and interiors and kitchen and table — and each of those trades wants a different form of the same material.
We quote each application in the unit that trade actually buys in, by the tonne, by the square metre or by the piece.
Durability and care
Hardness 5.5 (unexpanded glass); cleavage none; perlitic onion-skin fracture is diagnostic in the raw rock. That combination decides what it can safely be set into.
With no cleavage plane to worry about, the practical limit is abrasion rather than breakage, and it takes daily wear well.
Warm water, mild soap and a soft brush. Avoid ultrasonic cleaners on anything fracture-filled, stabilised, dyed or visibly included.
What perlite costs
Indicative pricing for perlite is $50-120 per tonne crude ore; expanded product $200-600 per tonne depending on grade.
That is a range, not a quote. Colour, size, clarity, cut and origin move the figure a long way inside it, and the only honest price is one given against a specific stone. Send us what you need and we will price it.
Questions
Is perlite treated, and how?
Crushed, graded and expanded in a vertical furnace. Uses: horticultural growing medium and soil conditioner, filter aid for beer, wine, juice and pharmaceuticals, lightweight plaster and concrete aggregate, cryogenic and building insulation, and as an abrasive filler. HEALTH: expanded perlite is amorphous and low in crystalline silica, which is its advantage over diatomite filter aids - but the crushing and expansion dust still requires nuisance-dust control, and some perlite ores contain minor cristobalite.
Where does perlite come from?
Milos and Kos, Cyclades, Greece - the largest world producer, Izmir, Erzurum and Nevsehir, Turkiye, No Agua and Socorro County, New Mexico, USA and Armenia, Hungary and Iran. Origin affects price, so we name the locality rather than the country on every quote.
Is perlite hard enough to wear every day?
Yes. At 5.5 (unexpanded glass) on the Mohs scale with no cleavage plane, it handles daily wear well. The practical limit is gradual abrasion rather than chipping.
How much does perlite cost?
Indicatively $50-120 per tonne crude ore; expanded product $200-600 per tonne depending on grade. Colour, size, clarity and origin move the price a long way within that, so treat it as a range and ask for a quote against a specific stone.
What is perlite confused with?
Most often Diatomite (the competing filter aid, with cristobalite risk), Vermiculite, Pumice (naturally expanded, no furnace needed) and Expanded clay aggregate. A refractive index of 1.48-1.50 and a specific gravity near 2.2-2.4 unexpanded; 0.03-0.15 bulk density expanded separate it quickly.
What is perlite used for besides jewellery?
heavy industry, filtration, architecture and interiors and kitchen and table. Each of those trades buys it in a different form and a different unit.
Related stones
Looking for perlite?
Tell us the size, the quality and what it is for. We source it, photograph it and quote it — with the locality named.
Ask about perlite