Sedimentary soil is made of physically weathered rock particles deposited by water or wind. Major types of these soils are limestone, chalk and tufa. Sedimentary rocks are the most common on the surface of the earth.
Calcareous soil is made of sediments with a significant amount of calcium carbonate. It has a fairly high pH and is alkaline, thus imparting acidity into grapes. Fossilized shells of sea life are weathered over time and break down to for calcareous soils.
Chalk is a white sedimentary soil that drains well and is not very heat retentive. It has a high pH level and encourages acidity to develop in grapes. Burgundy is famous for its chalk and limestone soils.
Limestone is made mainly of calcite and silica as well as some amount of sand, silt and clay. Decomposed ocean life creates calcite over millions of years. Limestone without a lot of other materials mixed in is white.
Alluvial Soil is formed over many years by the movement of water. Running water washes gravel, sand, silt and clay down its path. Alluvium washed down from the watersheds of adjacent hills will form an alluvial fan.
Benchland soil forms from alluvial deposits at the base of hills. Benchlands are often raised above the valley floor and contain much older alluvium. They are often leeched of nutrients and are porous from water percolation over the years.
Tufa forms when calcium rich bodies of water dissolve very slowly. When this occurs, calcium carbonates solidify in coarse formations. Tufa is useful as a construction material.
Igneous soil is formed from by lava flows below and above the earth’s surface. Volcanic soil is formed from molten lava and ash deposited above the earth’s surface. Plutonic rocks, such as granite, form deep underground.
Granite is composed of potassium feldspar, mica, hornblende and quartz. Granite has a high pH level and is alkaline. Acidity is imparted in grapes grown in these soils.
Basalt is formed as oceanic lava flows crystallize. Since much of California Wine Country is made of uplifted ancient oceanic crust, basalt is relevant to grape growing in the Golden State.
Pumice is molten rock that is spewed into the air and hardens in the atmosphere before falling back to the ground. It is made of phonolite, rhyolite and trachyte. These are all siliceous material.
Metamorphic soil is made from the weathering of schist, slate, or gneiss. These are all rocks that were originally sedimentary or igneous, but were transformed by pressure and heat underneath the earth’s surface.
Gneiss is a metamorphic rock that can be made of both igneous and sedimentary materials. Each type of gneiss is named based on its specific mineral composition.
There are many different types of schist that are also classified based on the mineral composition. These rocks are formed at lower a lower pressure and temperature than gneiss, and their grain is smoother.
Slate is a metamorphic rock that was originally an alluvial deposit subjected to great pressure and heat. It is chemically inert and resistant to weathering. Delicate grapes valued for pure varietal characteristics and that are made in stainless steel tanks are grown in these soils.
Marble is made from limestone and dolostone that have been metamorphically altered. Limestone that contains very few impurities makes white marble.
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