ROCKS OF TURKEY

Everyone who loves nature has brought back pebbles or lumps of rock at one time or another, unable to resist their colours or shapes. You see them in aquariums or the more colourful and crystalline ones displayed in cabinets. When by the seaside we have all searched for flat pebbles to send ricocheting over the water. For climbers craggy rock cliffs are as irresistible as they are intimidating, and they will strive sometimes for years until they have mastered a particularly difficult route. Stonemasons look at rocks with a different eye as potential blocks to be carefully hewn into shape.

Whatever your interest in rocks and stones might be, have you wondered how they came into being? Do you know how many million years a single step over rocks represents in the evolution of the earth? Have you wondered about their structure? What would you think if they told you that a black rock you hold is actually composed of multicoloured minerals?

Rocks are made of inorganic substances known as minerals. Every kind contains different minerals depending on its position of origin in the eath'sn magma, and each mineral has different physical and optical characteristics. Minerals reflect the physicochemical characteristics of the environment in which they formed. Crystalisation shows that they cooled slowly under ideal physicochemical conditions. Olivine or pyroxene minerals, for instance, are geological evidence that the rocks containing them formed many kilometres beneath the eath'st surface. Orthoclase, a type of feldspar, on the other hand formed much nearer to the surface.

Since rock formed at great depths cools slowly, it consists of large particles, while the minerals contained in volcanic rock formed on or near the surface cool quickly and therefore consist of fine particles. The minerals contained in metamorphic rock have been subjected to heat and pressure, and therefore form trailing parallel lines within the rock.

When examined under a microscope minerals which appear black or dark coloured are completely transformed. The polarised light striking the specimen from below reveals a rainbow of colours which constantly change with the slightest adjustment of the microscope , and we discover that these minerals sometimes form patterns which are extraordinary works of art.Since the first stone age artists who painted pictures of animals on cave walls, mankind has produced countless great painters and sculptors who have enchanted us with their work. They have often been inspired by nature, and when you look at the minerals which are the building stones of rocks through a strong microscope and see the wondrous geometric patterns they form at micron level, you might conclude that perhaps nature is the greatest artist of all.

* Yildirim Güngör
is a lecturer in Geological Engineering at Istanbul University

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