GEOMIMETICS

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Geomimetics is the term given to replicating the synthesis of minerals in the laboratory. Minerals are chosen for their interesting, unusual, and valuable properties, such as ion exchange, catalytic properties, colour shade and intensity, or magnetic properties, which can be tailored by compositional and structural modifications to create improved materials. It is analogous to biomimetics- i.e. chemists developing new organic compounds by copying and enhancing natural ones.

The cuboctohedral sodalite cavity is shown in blue surrounding a central anion (magenta) and four cations (orange)

A prime example of geomimetics is the synthesis and chemical modification of the mineral, lapis lazuli. It has a structure based on the simplest zeolite, sodalite, which consists of an aluminosilicate framework encapsulating the intense blue polysulphide anion radical, S₃^-·.

At the beginning of the 19^th Century, painters did not have an unfading, inexpensive, consistent and vivid shade of blue on their palette. The best blue pigment was ultramarine, derived from lapis lazuli, but the rarity of lapis lazuli made ultramarine too expensive for most painters. Jean-Baptise Guimet and Christian Gmelin both independently developed ways of producing cheap synthetic ultramarine in the late 1820s using clay minerals, sulphur, pitch and sodium carbonate. Today, synthetic ultramarine has been developed further to produce new pink and violet shades by chemical modification of the encapsulated S₃^-· radical post synthesis and is used commerically in ceramics, plastics, cosmetics and paint.

For tens of thousands of years man has utilised rocks and minerals. Originally they were used to build shelters, as weapons for hunting or as pigments for paint and jewellery. In the 21^st Century, geomaterials, minerals and their closely related synthetic analogues, are employed in a variety of key industrial applicactions as described in the table below. Geomaterials are quite literally a natural choice when searching for new industrial materials in today’s environmentally conscious era as they are already part of man’s environment.

Applications of selected minerals and their synthetic analogues