Geology: Minerals

Appears in

Oxford Companion to Wine

Oxford Companion to Wine

By Jancis Robinson

Published 2006

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Minerals in geology, minerals are natural, inorganic solids in which the constituent atoms have an ordered, systematic structure. (In the nutrient sense, minerals are soluble single elements.) The two most abundant elements in the outer part of the Earth are oxygen (46%) and silicon (28%), consequently the most common minerals are various silicates, in which the two elements are rigidly bonded together, alone in the case of quartz (silicon dioxide) but usually with a number of other elements.

Some minerals relevant to vineyard geology are not silicates but are composed of a single element, such as carbon (the mineral graphite), largely responsible for the colour of rocks such as dark shales; and sulfur, found in volcanic areas. Non-silicate compounds include the oxides (e.g. hematite, the iron oxide giving the distinctive red colour of terra rossa) and sulfates such as gypsum. Especially important are the carbonates, particularly calcium carbonate (the mineral calcite). Materials dominated by calcite, such as limestone and marl, are described as calcareous.