Natural Pozzolan

What natural Pozzolan actually is

The species behind natural Pozzolan is volcanic ash, tuff and pumicite that reacts with lime in the presence of water to form cementitious compounds - the original hydraulic binder, and now a major route to lower-carbon concrete, Amorphous aluminosilicate glass, SiO2 45-70% with Al2O3 and CaO; reactivity depends on glass content, not bulk chemistry; it forms in the amorphous system.

Grey, buff, pink and black depending on iron and oxidation; colour is a real consideration for architectural concrete is responsible for the colour — and the chromophore, not the name, is what decides whether a colour is stable.

On the instruments it reads a refractive index of 1.48-1.55 (glass) and a specific gravity of about 2.20-2.60, with none cleavage.

Where natural Pozzolan comes from

Commercial material comes from Pozzuoli and the Phlegraean Fields, Campania, Italy - the Roman source that gave the material its name, Santorini, Greece (Santorini earth, used in the Suez Canal works), Rhineland and the Eifel, Germany (trass), Utah, Nevada, California and Arizona, USA and Turkiye, Iran and Mexico.

Different localities give different colour and different clarity, and the trade prices them differently. We state which one.

How natural Pozzolan is treated

Dried, milled and classified; some producers thermally activate marginal material. Uses: supplementary cementitious material in concrete, reducing Portland clinker content and therefore CO2; also improves sulphate resistance and suppresses alkali-silica reaction. COMMERCIALLY SIGNIFICANT RIGHT NOW: fly ash and blast-furnace slag supply is falling as coal plants close and steelmaking changes, so natural pozzolans are being brought back into large-scale use for the first time in a century, and new deposits are being permitted in the western USA. Roman marine concrete made with Pozzuoli ash has survived 2,000 years in seawater, which is not a marketing claim but a well-documented materials-science result.

We state the treatment on every stone, including when the honest answer is that it cannot be determined. A treatment disclosed is a fact; a treatment discovered later is a refund.

What natural Pozzolan is confused with

Watch for Fly ash and ground granulated blast-furnace slag (the declining industrial SCMs), Calcined clay / metakaolin (the manufactured competitor, LC3 cement), Silica fume and Limestone filler — these are what turn up sold under this name.

The separation is rarely a matter of opinion: refractive index 1.48-1.55 (glass) and specific gravity 2.20-2.60 settle most of it in a minute, and magnification settles the rest.

What natural Pozzolan is used for

The trades that buy natural Pozzolan are heavy industry and architecture and interiors. They do not want the same thing, and they do not pay in the same unit.

We quote each application in the unit that trade actually buys in, by the tonne or by the square metre.

Durability and care

Hardness Variable, 3-6 as a rock; supplied as a powder; cleavage none. That combination decides what it can safely be set into.

Below about 5.5 a stone will be scratched by ordinary household dust, which is largely quartz. That does not make it unusable — it makes it a pendant, an earring or an object rather than a ring worn every day.

Warm water, mild soap and a soft brush. Avoid ultrasonic cleaners on anything fracture-filled, stabilised, dyed or visibly included.

What natural Pozzolan costs

Expect roughly $30-90 per tonne milled and delivered, competitive with the fly ash it replaces, depending on quality.

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.

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