Clay [sec. XIV; latin argilla] is a type of fine-grained natural soil material that contains hydrous aluminium phyllosilicates (clay minerals) that develops plasticity when wet. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure. Clays are plastic due to particle size and geometry as well as water content, and become hard, brittle and non–plastic upon drying or firing. Depending on the soil's content in which it is found, clay can appear in various colours from white to dull grey, brown to deep orange-red or green.
From a grain size point of view, the clays are made up of two fractions, a coarse and a fine one. In the coarse fraction, made up of the same minerals that make up the sands, the granules are between 1/16 and 1/256 mm in size; in that end, made up of clayey and clayey-micaceous minerals, the dimensions are even smaller. Depending on whether the coarse or fine fraction prevails, we speak of silty clays (silt) or fine clays, which correspond (in the terminology used in the refractory and ceramics industry) respectively to lean clays (rich in sandy skeleton) and fatty clays (poor in sandy skeleton). Most of the clays have sedimentary origin, deriving from the deposit and accumulation of the finest turbids transported in suspension by the surface waters.
GEOLOGY OF CLAYS
Clay minerals are typically formed over long periods of time by the gradual chemical weathering of rocks, usually silicate-bearing, by low concentrations of carbonic acid and other diluted solvents. These solvents, usually acidic, migrate through the weathered rock after leaching through the upper weathered layers. In addition to the weathering process, some clay minerals are formed by hydrothermal activity deriving from the transformation of eruptive rocks by hot water of deep origin.
Clay deposits may be formed in places as residual deposits in soil, but thick deposits usually are formed as the result of a secondary sedimentary deposition process after they have been eroded and transported from their original location of formation. Clay deposits are typically associated with very low energy depositional environments such as large lakes and marine basins.
Primary clays, also known as kaolins, are located at the site of formation. Secondary clay deposits have been moved by erosion and water from their primary position.
The sedimentation environment is generally marine, deltaic areas or not far from them; however, we are led to admit that almost all marine clays have undergone re-sedimentation phenomena, thus accumulating in areas relatively far from those of the original deposit. Less frequently the sedimentary environment is continental in nature. In the sedimentation of fine clays, the phenomena of flocculation are very important, regulated by the chemical-physical conditions of the waters and particularly by the presence of electrolytes. During transport in a continental environment, the clayey material is suspended; when it reaches a marine basin (or lagoon or lake) with a high concentration of substances in solution, the finer granules gather around the electrolytes, forming micelles that sediment rapidly. This phenomenon explains why clay deposition usually occurs in delta regions or in the immediate vicinity.
A particular type of residual clay is the FERRETTO (reddish in color due to the presence of aluminum and iron hydroxides) of the Italian Prealps, which derives from the meteoric alteration of the moraine and fluvio-glacial deposits of the Quaternary age. The group of transported clays is much larger and their distinction is made in relation to the sedimentation environment: glacial, if they have accumulated in lake basins on the edge of glacial regions; river, when they were deposited by the floods of rivers; lakes, lagoons, marinas.
As you move away from the place of erosion, you will notice a clear evolution in the resulting deposits, in the sense of a more pronounced argillification of the sediment. Thus, for example, in the glacial and river clays the characteristic minerals of the clays are present only if clay deposits emerged in the area eroded by the glacier or the river.
Calcium carbonate is frequent in marine clays, both from direct chemical precipitation and from organic sources; when less than 25% is present, calcareous clays occur; between 25 and 75% go from marly clays to marls; over 75% to clay limestones. In some types of clay it is possible to have a significant quantity of silica, deriving from chemical precipitation and not from quartz debris or from siliceous organisms: for a percentage increase of silica we pass to porcelain. Particular varieties of marine clays are black clays, whose color is due to the presence of organic substances and sulphides of gypsum and which are the result of slow deposition in calm environments; and red clays, whose color is given by the presence of iron oxides and hydroxides and which are deposited in large areas of the ocean floor (abyssal red mud).
USES
Clays exhibit plasticity when mixed with water in certain proportions. However, when dry, clay becomes firm, and when fired, permanent physical and chemical changes occur. These changes convert the clay into a ceramic material. Because of these properties, clay is used for making pottery, both utilitarian and decorative, and construction products, such as bricks, walls, and floor tiles. Different types of clay, when used with different minerals and firing conditions, are used to produce earthenware, stoneware, and porcelain. Prehistoric humans discovered the useful properties of clay. Cooking pots, art objects, dishware, smoking pipes, and even musical instruments such as the ocarina can all be shaped from clay before being fired.
Clay tablets were the first known writing medium. Scribes wrote by inscribing them with cuneiform script using a blunt reed called a stylus. Purpose-made clay balls were used as sling ammunition. Clay is used in many industrial processes, such as paper making, cement production, and chemical filtering. Until the late 20th century, bentonite clay was widely used as a mold binder in the manufacture of sand castings.
Studies in the early 21st century have investigated clay's absorption capacities in various applications, such as the removal of heavy metals from waste water and air purification.
COSMETICS
The most common and well known use of clay is in cosmetic industry, infact clays can be divided also by shade, so we have green, white, red, yellow, gray clay, blue clay and beige clay. The color depends on the age of the clay, the origin of the deposits and its chemical composition.
The most common are:
Red clay
Red clay is rich in iron and low in aluminum. The coloring of this type of clay is due to the presence of trivalent red iron. The role played by red clay has changed over the centuries, if it was used by the ancient Romans to combat joint pain, to treat horse wounds and in washing to protect livestock from infections, today it is mainly used in the field of cosmetics natural. At home we can use red clay to prepare very delicate masks and beauty creams suitable for those with very sensitive skin with dermatitis problems.
Green clay
Green clay contains about 50 percent of silica and 14 percent of aluminum is the clay most used in cosmetics. It has a slightly alkaline pH and high anti-inflammatory properties. Thanks to its strong absorbing power, it is used for skin care, in particular for the treatment of acne and eczema. Green clay has purifying and detoxifying properties. It stimulates good circulation and has a high absorbent power so it is less suitable for those with dry skin.
White clay and gray clay
White clay and gray clay have similar properties. Gray clay, with its 60 percent silicon and 20 percent aluminum, has a strong anti-inflammatory and anti-acid action. Even white clay can reach up to 60% of siliceous compounds and as mentioned, they have similar properties. Those who have very dry skin and do not even tolerate red clay should try white clay.
White clay can count on a high percentage of silicon (about 48 percent) and aluminum (about 36 percent), these are the two elements that give it its characteristic color. The first deposit of white clay was discovered in the Chinese region of Kao-Ling and because of its origins, white clay is also called kaolin. Just mix the white clay with warm (or warm) water to obtain excellent mud for the skin. The masks based on white clay: • purify the pores • detoxify the skin • soothes irritated skin • is a natural cure for acne
TO LOG THE CACHE
At posted coordinates you will find a particoular phaenomena appening at the base of rock wall. Observe it and answer to the following questions by message without attached them to the log:
1) Is the wall dry or wet?
2) Here you can see the clay. As you learnt from the listing, is this a primary or secondary clay?
3) Which color do it has?
4) Enjoy your free beach SPA and post a photo of you with your treatment on or your nickname in front of the sea!
Is not necessary to wait my ok to log the cache.
RELAX AND HAPPY CACHING!!
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