Tuesday, July 12, 2011


Sepiolite has been known since Roman times when it was used to filter and purify wine. No other mineral is known to absorb more water or other liquids as efficiently as sepiolite, which is why sepiolite is commonly used in cat litter. Sepiolite is also used to absorb liquid spillages, such as in oil spills, and odours and stabilise aqueous products like paints, resins and inks.
Sepiolite is an aluminosilicate clay mineral with a typical formula of Mg4Si6O15(OH)2·6H2O.

Sepiolites absorb moisture by using tiny tunnels in the crystals. The elongated, needle-shaped sepiolite crystals pack very loosely into a lightweight porous material. The surface area ranges between 75 and 400 m2/g, meaning that 20g of mineral have an internal surface equivalent to that of a football court. This is why sepiolite can absorb 2.5 times its weight in water. The tunnels in the crystal structure along with the empty space between the needles form a capillary network through which liquids can easily flow deep inside the bulk where the molecules attach to the surface of the crystals.

A team of scientists from Spain and France has obtained, for the first time, single-crystal X-ray diffraction images of sepiolite, opening the path to industrial synthesis and further improvement of its properties. In synthetic form, sepiolite could bind food products and stabilise drugs, extending their shelf life and making sepiolite an edible product.

Manuel Sanchez del Rio, Emilia Garcia-Romero, Mercedes Suarez, Ivan da Silva, Luis Fuentes Montero, and Gema Martinez-Criado. Variability in sepiolite: Diffraction studies. American Mineralogist, 2011 DOI: 10.2138/am.2011.3761

Further Reading
Percentage Composition
Balancing Chemical Equations

Study Questions
  1. Calculate the percentage composition of sepiolite, Mg4Si6O15(OH)2·6H2O
  2. Explain what the ·6H2O part of the formula refers to.
  3. Write a balanced chemical equation for the dehydration of hydrated sepiolite to form anhydrous sepiolite.
  4. Calculate the maximum mass of water you could obtain from 1kg of hydrated sepiolite.
  5. If the sepiolite in question 2 has a surface area of 200m2/g, what is the total surface area of the sample in question 4?
  6. Use the equation in question 3 to explain why sepiolite is used in cat litter.
  7. Sepiolite is an aluminosilicate mineral. Explain what is meant by the term aluminosilicate.
  8. Sepiolite is sometimes referred to as a zeolite-like mineral. In what ways is sepiolite similar to a zeolite mineral?

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