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Vineyards, Rocks, and SoilsThe Wine Lover's Guide to Geology$
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Alex Maltman

Print publication date: 2018

Print ISBN-13: 9780190863289

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780190863289.001.0001

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PRINTED FROM OXFORD SCHOLARSHIP ONLINE (oxford.universitypressscholarship.com). (c) Copyright Oxford University Press, 2021. All Rights Reserved. An individual user may print out a PDF of a single chapter of a monograph in OSO for personal use. date: 23 September 2021

Weathering, Soil, and the Minerals in Wine

Weathering, Soil, and the Minerals in Wine

(p.159) 9 Weathering, Soil, and the Minerals in Wine
Vineyards, Rocks, and Soils

Alex Maltman

Oxford University Press

Weathering of rocks is the crucial first step in making vineyards possible. For where the debris produced by weathering–the sediment we met in Chapter 5–becomes mixed with moist humus, it will be capable of supporting higher plant life. And thus we have soil, that fundamental prerequisite of all vineyards, indeed of the world’s agriculture. So how does this essential process of weathering come about? Any bare rock at the Earth’s surface is continually under attack. Be it a rocky cliff, a stone cathedral, or a tombstone, there will always be chemical weathering–chemical reactions between its surface and the atmosphere A freshly hewn block of building stone may look indestructible, but before long it will start to look a bit discolored and its surface a little crumbly. We are all familiar with an analogy of this: a fresh surface of iron or steel reacting with moisture and oxygen in the air to form the coating we call rust. In his “Guide to the Lakes” of England, William Wordsworth put the effects of weathering far more picturesquely: “elementary particles crumbling down, over-spread with an intermixture of colors, like the compound hues of a dove’s neck.” A weathered rock is one that is being weakened, broken down. The rock fragments themselves are further attacked, which is why stones in a vineyard often show an outer coating of discolored material, sometimes referred to as a weathering rind (Figure 9.1; see Plate 22). If the stone is broken open, it may show multiple zones of differing colors paralleling the outer surface of the fragment and enclosing a core of fresh rock. Iron minerals soon weather to a powdery combination of hematite, goethite, and limonite, and the rock takes on a reddish-brown, rusty-looking color. The great example of such weathering in viticulture is the celebrated terra rossa, but the rosy soils in parts of Western Australia and places further east such as McLaren Vale and the Barossa Valley are also due to iron minerals. Several Australian wines take their names from this “ironstone.”

Keywords:   abrasion, bentonite, chlorine, goethite, limonite, loam, magnesium, nitrogen, phosphorus, sandstone

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