Pumice – complex geology in a familiar form

Pumice stone is the end product of an amazing natural force – the volcano.

As a natural ingredient it has some unique properties including low density, lightness and abrasiveness which make it ideal in exfoliating and polishing products.

From a marketing view point, pumice manages to combine scientific complexity with familiarity. Most people recognise a pumice stone as a humble household object – yet delving deeper into the scientific origins of pumice open up a much more complex picture requiring at least a superficial understanding of geology.

Volcanic rock varies enormously depending on the type of eruption that created it and the source and composition of the magma erupted. The cooled discharge from volcanoes can be anything from ash to sizeable rocks with small minerals in them.

Geologists use the criteria of appearance and mineral composition to categorise the rock spewed out of volvanoes based on both observations of hand specimens and microscopic study of wafer thin sections of rock.

Most consumers associate pumice with comforting bath time beauty routines. The pumice stone sitting in a traditional chrome bath rack has a homely, almost reassuringly old-fashioned quality.

Some volcanic rock – like pumice – has ‘holes’ or vesicles within the rock which are caused by gas discharges during more violent eruptions. Pumiceous rock is extremely light and full of holes because it is the product of an extremely forceful volcanic eruption.

Pumice was heated to incredible temperatures during eruption and became almost completely liquid. Subsequent cooling was so rapid that there was no time for the pumice to crystallize. Rapid cooling solidified the gas dissolved within the molten mass and the frothy liquid turned to stone.

Small pariticles of minerals are contained in most pumices but too great a quantity of mineral desposits actually degrade the commercial quality of the pumice making it overly hard.

Pumice varies in colour according to its mineral composition. Rhyolite and trachyte pumices are white and contain 60 to 75% of silica; andesite pumices are often yellow or brown; while pumiceous basalts are pitch black when perfectly fresh.

Pumice can be formed from any type of lava given the right conditions but in reality pumice occurs most often where the lava is acidic.

High quality pumice is found in Iceland, Hungary, Nevada, Teneriffe, New Zealand, Pantellaria and the Lipari Islands. The highest quality and most costly pumice has regularly shaped and sized steam cavaties and is free of minute crystals.

As the demand for pumice has grown – environmental concerns about the over extraction of the rock from traditional sources has risen. Newer sources of pumice have emerged with rich deposits of pumice stone in other vast mining areas like California and Nicaragua. With the increased focus on natural skin care, the demand for pumice is unlikely to decrease.

The combination of geological complexity with familiarity in a naturally effective ingedient make pumice stone a winning ingredient for the cosmetic formulator in the future.

(Read further information about the origins and classification of pumice)

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