The upper
part of the soil profile is composed of drift material containing
some residual loess. The soil of the plough horizon soil consists
of silt and humus as well as larger fragments of sericite gneiss
and quartzite. This drift material covers the upper horizon
of the naturally developed residual loess-containing cambisol.
The sandy subsoil of this cambisol contains no residual loess
and is composed of broken down sericite gneiss rubble and fine-grained
products of the weathering processes.
The
presence of stones and rubble restricts the water holding capacity
of the soil. However, this moderate water reservoir is capable
of supplying plants with adequate amounts of water. In fact the
water supply to the vines is excellent. Sericite gneiss is only
found in the higher altitudes of the Rheingau. These locations
receive more rain and are cooler than those at lower altitudes.
Although
the subsoil is rather dense, the roots can penetrate deep into
the acid residual derived from the weathering of the sericite
gneiss. This contains a rich supply of iron and manganese but
very little mineral nutrients. The vines obtain their nutrients
from the loess-containing plough horizon. The grape ripening
conditions are good if an adequate nutrient supply is maintained.
THE ROCK
This light greenish-grey foliated rock outcrops near Hallgarten,
Kiedrich and on the Neroberg in Wiesbaden. This rock represents
the remains of Silurian volcanoes (between 445 and 415 million
years ago). The slow cooling of magma deep in the Earths crust
allowed some minerals to form large crystals. During an eruption
the magma together with these crystals were rapidly transported
to the surface. Here the remaining liquid magma cools rapidly
and crystallizes into microscopically small crystals. This results
in a rock consisting of large crystals dispersed in a fine groundmass.
The visible crystals are called phenocrysts. This specific rock
texture is called porphyry. In this case the magma was quartz-rich
or felsic. The solidified magma is a rhyolite, which has a similar
chemical composition to the plutonic rock granite. During the
formation of the
SERICITE
GNEISS
Hortic
anthrosol – cambisol formed on residual loess
over sericite gneiss – a
fresh,calcium
carbonate-free location, low on base nutrients with
moderate ripening
condi- tions.
Vineyards
high above the city – the
Neroberg in Wiesbaden consists of ancient sericite
gneiss.
Sericite
gneiss in thin section. The porphyric texture
of a metamorphic igneous rock is characterised by large quartz
phenocrysts in a fine-grained ground- mass.
SOIL
PROPERTIES
medium
soil water capacity
moderate
rootability
moderate
aeration
moderate
warming capacity
no
calcium carbonate (acid)
low
mineral nutrient potential
Rhenic Slate Mountain
Range, the rhyolite was exposed to higher temperatures and
pressures deep in the earth’s crust. Under these conditions
the rock texture was changed in a process called metamorphism.
The resultant rock is called a meta-rhyolite or sericite gneiss
and consists of quartz and alkali and plagioclase feldspars.
Therefore the rock is a rich source for potassium or sodium.
