Sand is a free-flowing friable mixture consisting of small grains that are formed as a result of the natural destruction of rocks. widely used in construction and industry. It has various technical characteristics, primarily due to its origin.
Some features of the sand
Raw sand is mined mainly in quarries. Such material has a high content of clay particles and other impurities, so it is suitable only for sprinkling under the foundation of construction sites.
Sand treated with a large amount of water is called "alluvial". It contains a minimum amount of impurities. Such sand already has completely different technical specifications. It is used for masonry, in plastering, for the construction of foundations. With its help, paving slabs and concrete products are also produced.
Types of sand and their main characteristics
According to the place and method of extraction, sand is of three types:
Most often quarry sand has yellow and gray-yellow color. Clay and other substances are removed from it in two ways - by washing and sieving. Screened sand is somewhat inferior in quality to washed sand, since there are more impurities in it. For this reason, seeded sand is not used for the production of concrete products, which may crack as a result of exposure to low temperatures.
River sand taken from different rivers, as a rule, has its own shade and can be yellow, brownish, gray or light gray. White river sand is less common. Nature itself, through natural washing with water, made sure that clay and other particles were contained in its composition in a minimum amount. Such sand has a very wide range of applications and is a versatile material. It is used in the production of artificial stone, concrete and sand concrete, paving slabs.
Quartz sand owes its origin to the crushing and destruction of natural quartz. It is a milky white material, however, it can be easily dyed any other color. Quartz sand has a homogeneous composition and is a harder substance than other types of sand. It is also distinguished by the ability of sorption and chemical inertness. In addition to construction, this material is used in the production of glass, in the operation of water purification facilities.
There is a well-established opinion that it is quite easy to choose sand: I ordered building sand - here you have a raw material component for concrete, and a backfill for a path. But this opinion is wrong. Since there are several varieties of sand, which have their own distinctive characteristics, and are used in certain work.
Classification
So, according to the place of origin, sand is usually classified into the following types:
river sand
River sand is mined from the bottom of rivers. It is characterized by natural purity and good culvert qualities. The grain size of river sand is from 0.3 to 0.5 mm.
This type is used for the preparation of concrete solutions, cement screeds, treatment filters, drainage structures. It should be noted that when preparing a concrete mixture, this type of sand settles quickly, so the solution must be constantly mixed. The cost of river sand is from 600 to 800 rubles per 1 m 3.
Quarry sand
Quite logically, quarry sand is mined by an open method and includes impurities in its composition: dust particles, stones. Sand grains of quarry sand are much smaller than those of river sand, their sizes range from 0.6 to 3.2 mm.
In its original raw form, building material can be used for trenching or as a sprinkle under the foundation. Typically, leading manufacturers wash and screen quarry sand. In this case, it can be used when performing plastering and finishing works, to create an asphalt concrete mixture, to form a screed.
Sea sand
This non-metallic mineral is extracted from the bottom of the sea using hydraulic projectiles. There are practically no impurities in it, and salt is involved in purification.
This type of sand is considered the most popular. It is used everywhere, from the creation of concrete structures to the formation of fine dry mixes. But, despite the unique characteristics of this building material, there is a shortage in it, since it cannot be mass-produced.
Sometimes building sand is considered a separate species. But, as a rule, it means both river and quarry sand. River sand can be of two colors - yellow and gray, and quarry - brown and yellow.
But it turns out that in nature there is also black sand that shines like metal. He may be found in different corners the globe. And this type of sand is formed as a result of geological processes.
This mineral consists of dark-colored heavy minerals and is formed by washing out light components. The main minerals are magnetite, ilmenite, and hematite.
Such sands are characterized by high radioactivity - 50-300 microroentgens per hour, but sometimes this parameter can reach a thousand microroentgens per hour. Due to the high radioactivity, this mineral is not used in construction and economic activities.
artificial sand
It is worth noting that the above types of sand are natural, as they were formed by the natural destruction of rocks. But, the market has artificial sand, created by crushing marble, limestone, granite.
The most popular among artificial types of sand is quartz. It is made by grinding and dispersing the white quartz mineral until a homogeneous fraction is obtained. From natural species sand, it is distinguished by the fact that it does not contain impurities and has a homogeneous composition. These advantages make it possible to accurately calculate the parameters of a structure made on quartz sand.
The color of sand depends on the predominance of one or another mineral in its composition and can be white, light gray (quartz sand), green, greenish gray (glauconite-quartz), pink, pinkish gray (arkose), gray, dark - gray, greenish (graywacke sand), brown of varying intensity and various shades (other polymictic sands).
Conditions of education and stay. Sands occur in the form of layers and lenses among other sedimentary rocks and are products of physical and chemical weathering of various rocks, prolonged and repeated washing and sorting of detrital material by flowing waters or sea surf, and sedimentation at the bottom of reservoirs. Polymictic varieties are ubiquitous. there are deposits of oligomictic (quartz) sands in the Leningrad region. (Sablinskoye on the Tosna River, Kolchanovskoye on the Syas River, in the upper reaches of the Luga River and in the vicinity of the Luga Mountains), in Valdai, in the Bryansk Region, in many districts of the Voronezh (Latnetsskoye), Kursk and Moscow Regions , in the Donbass (Chasov-Yarskoe), in the North. Caucasus (Kayalskoye), in the Urals (Kasli and Magnitogorsk districts), in the East. Siberia (Tulunskoye), etc.
Diagnostics. Varieties of sands are determined by the mineral composition of detrital grains. To clean their surface from films of iron hydroxides and other secondary products, it is recommended to wash the sand in water and in dilute hydrochloric acid.
Practical value. Essentially quartz sands are used as a raw material for the glass industry, in the production of sand filters, silicate bricks, cement mortars, plasters, as well as carborundum (a highly hard compound of silicon and carbon) and ferrosilicon (an alloy of silicon with iron); as an abrasive material in sandblasting machines and for sawing rock monoliths of low and medium hardness (limestone, marble, etc.); as a molding material in the foundry business. Glauconite-quartz sand contains up to 6% K20 and is a valuable potash fertilizer. Polymictic sands are widely used in road construction. Alluvial deposits of gold, platinum, diamonds, cassiterite, columbite, etc. are associated with river sand deposits. Ancient and modern " sea sands associate placer deposits of ilmenite, magnetite, zircon, rutile, etc.
Loess
Name from him. Loss - cliff, due to the ability of the rock to form specific landforms - stable sheer cliffs, deep canyons with vertical walls. A synonym is aleurite, (from the Greek a^supov - flour).
characteristic signs. Dusty rock (fine earth), consisting of clastic particles 0.1-0.05 mm in size, indistinguishable to the naked eye. Non-layered. Lightweight, porous. Light yellow or light brown. Very soft, easily rubbed with fingers into a fine powder; while the presence of grains of sand is not felt. Feels dry (not greasy). Boils under the action of HC1. Carbonic lime is concentrated in the loess in the form of figured nodules - "dutiks" (hollow) or "cranes". Sometimes there are shells of terrestrial molluscs, bones of mammals. It gets wet in the water.
Conditions of education and stay. The result of the accumulation over many millennia of dusty material, lifted into the air and carried over vast distances by desert winds and sandstorms in hot climates. Layered and denser loess-like loams analogous to loess are formed on a much smaller scale as a result of elutriation and leaching of fine-grained material by flowing waters on the slopes of uplands or in floodplains of rivers.
Loess is distributed over vast territories bordering the Central Asian deserts. In the southwest and south European Russia it lies in the form of a powerful layer directly under the soil.
Diagnostics. Easily determined by the above physical properties, behavior in water and interaction with HC1.
Practical value. The soil formed on the loess is highly fertile when artificially irrigated. The high porosity of loess, its ability to absorb water and turn into a mobile mass capable of flowing (quicksand) cause great difficulties in the construction of buildings and underground structures (subway tunnels, etc.) in moist loess soil.
RECOMMENDED LITERATURE for an independent deeper acquaintance with the basics of mineralogy and petrography POPULAR SCIENTIFIC LITERATURE Fersman AE Entertaining mineralogy. M.-L., 1953; M., 1959. Fersman A. E. Entertaining geochemistry. Ed. …
Mineralogical Museum. A. E. Fersman of the Academy of Sciences of the USSR. Moscow, V-71, Leninsky Prospekt, 14/16. Moscow State University M. V. Lomonosov (Moscow State University). Earth Science Museum; Department of Mineralogy and Petrography of the Faculty of Geology. …
E. BY RADIOACTIVITY I. Highly radioactive Gatchettolite Carnotite Otunite (otenitis) Torbernite Uraninite, pitchblende II. Weakly radioactive Columbite-tantalite Lovchorrite, rincolite Perovskite, loparite Pyrochlore-microlite Titanium-tantalum-nobates Zircon (cyrtolite, malacone) Contents of the book - Minerals ...
In uncovering and reviewing the history of our planet, geologists are faced with a fascinating scenario written by nature. The history of the development of the Earth is a colorful and vibrant performance full of dramatic events, many of whose participants and spectators have long since gone into oblivion, leaving their mark on the earth's layers. Every layer, every layer earth's crust is like a page of a huge stone book. On these pages, in a peculiar language in the form of prints of plants and fossil remains of animals; traces of storms that swept over the Earth, events that took place on the Earth and in its bowels many hundreds of millions and billions of years ago are recorded.
Like criminalists, geologists slowly and scrupulously, step by step, find and study facts, build various hypotheses (assumptions, conjectures) and recreate pictures of the distant past from non-existence. For several centuries, natural scientists and geologists have been trying to reconstruct the history of the Earth. But it is still full of mysteries.
The innumerable riches of the subsoil - coal and brown coal, iron, manganese, aluminum, copper and other ores, gold, marble and many building materials have always aroused great interest among people. Adult people always find a use for these riches.
It's always interesting to see what you can get. How to use these riches for the benefit of all mankind.
Curiosity. It all starts with him.
For example:
For many decades, millions of boys and girls have been playing with great pleasure in a simple, but terribly exciting and interesting game.
It's yellow and fluffy
Heaped in the yard.
If you want, you can take
And play with friends.
It is impossible to find a person on Earth who does not know what it is: sand. For some, sand has become a game, for some, a cure, and for some, a tragedy.
And yet, what is it?
Every summer, with great pleasure, I spend time in one of my favorite places - the sandbox. From early childhood, I was fascinated by these tiny grains of sand, which, if one gets into the eye one by one, it will be very unpleasant, but if one by one they are added together, one can create unique figures.
When it is dry, it flows like a river, and if it is moistened with water, it becomes sticky like snow.
Looking into the explanatory dictionary of S.I. Ozhegov, I found that sand is loose grains of quartz or other solid minerals. (S. I. Ozhegov Dictionary of the Russian language., ed. >, M., 1973).
In > V. I. Dahl, I read that >.
The explanatory dictionary of the Russian language D. N. Ushakov gives the following definition: >.
From everything I read, I realized that sand is a product of the destruction of various rocks. According to the size of the grains, they distinguish: crushed stone, gravel, coarse, fine sand and sand dust. According to the location, sand can be: river, sea (dunes), ravine, mountain. By composition - quartz, calcareous, magnetic, gold-bearing. That's why he's so popular. And it is used almost everywhere.
Let's consider everything in order.
And so: What is sand?
No, not sugar, but the one on which it is so pleasant to lie on a hot summer day. Especially if it's not just sand, but a beach.
When a solid rock was exposed to wind, rain and frost, it broke into small pieces. If these particles are small enough (from
0.05mm to 2.5mm in diameter), they are called sand.
So, sand is what is left of rocks, boulders, ordinary stones. Time, wind, rain, sun and time again destroyed mountains, showered rocks, crushed boulders, crushed stones, turning them into billions of grains of sand, making them sand. So our favorite river, sea and other sand consists of quartz, feldspar and mica.
Since sand is the small particles of minerals that make up mountains, any minerals can be found in the sand. The main material of which sand is composed is quartz. Some sands contain 99% quartz. Other minerals that can be found in the sand are calcite, mica, iron ore, in small quantities - garnet, tourmaline, topaz.
Sand can be found wherever mountains are exposed to nature. One of the places with the greatest occurrence of sand - seaside. Here the impact of the tides, their destructive effect on the mountains, the friction of the applied sand on the mountains and the dissolution of some mountain minerals with salt water affects. All this together contributes to the formation of sand.
But where do the sands in the deserts come from?
Much of the sand is blown into the desert. In some cases, desert sand is formed by the destruction of mountains. There are cases when deserts were originally the seabed, but millennia ago the water receded. The bare sands of deserts that can move are called dunes.
Sand - very useful material. It is used in the manufacture of concrete, glass, sandpaper, filters for water purification.
Since sand is 99% quartz, then: What is quartz?
Every day we use quartz in everyday life and do not even think that it is quartz. Quartz is very widespread and has a huge application.
Quartz is also called silica. It is made of silicon and oxygen, heavier than steel and stronger than glass.
Without impurities, quartz is colorless or white, various additives make it red, brown, green, blue, blue, even black. Sometimes quartz is found in the form of large transparent hexagonal crystals with sharp ends - this is >.
Most mountains are made of quartz. Sandstone is made up of quartz particles held together by a cementing compound. Granite also contains quartz. White sands are pure quartz. Plain sand is also mostly quartz! Many of the semi-precious stones are also quartz, colored with various impurities. For example, agate, amethyst, onyx.
Why is the sand different colors?
There is a lot of sand on earth. It is enough to imagine sandy deserts, in which mountains of sand (dunes) sometimes stretch for tens and hundreds of kilometers, or sea coasts with sand dunes intertwined by the wind, if they are not held together by pine roots. In the deserts Central Asia and Kazakhstan, the sands occupy at least a million square kilometers.
The color of the sand is different - black, greenish, reddish, although yellow and white sand is most common. The color of sand depends on its origin. Sand appears after the destruction of solid rocks under the influence of temperature fluctuations, wind or water. This process is especially intense in the zone of constant sea surf or rapids. mountain rivers. The resulting sand is grayish in color, like most types of granite.
Coastal cliffs gradually break up into separate blocks, which turn into stones and pebbles by waves. For many years, waves rub them against each other and gradually crush them into ever smaller particles. They are also hewn and gradually turn into a mass of a homogeneous particle size. Often, small pieces of corals and shells crushed by the sea are added to it.
Sometimes sand is brought to the coast by the winds. Such, for example, is the composition of the coast mediterranean sea where the sand is blown in from the Sahara Desert. Such sand has a bright yellow color and consists of small pieces of quartz. Pink sands are made up of feldspar. The red ones are from garnierite.
Some beaches are made up of only one color of sand, such as the black lava beaches in Tahiti. White sand, consisting of the remains of coral and shells, is found on atolls and the coasts of tropical seas. In Europe, it can be seen in fossil deposits, almost entirely composed of calcareous compounds.
There are amazing black sands in Azerbaijan, near the city of Lankaran. They were formed from the deep, black color of the gabbro rock.
But much more often the sands are a mixture of colors, since they consist of different types of rocks with an admixture of fragments of coral and shell rock.
We have learned a lot of good things about sand, and it seems that there is nothing more important and valuable on Earth than sand. It seems that life without sand would be boring and difficult. But why then are many so afraid of such a wonderful and irreplaceable sand?
Why is he so scary? Damage caused by sand.
On Earth, more than half of the land surface is deserts and steppes. In these spaces, sandstorms are born, develop and rage. There is a place where they can roam with all their might!
As soon as the morning rays warm the earth, the winds begin their work: they carry a huge amount of dust, pour and rewind millions of tons of sand. And travelers are poisoned by existence, because neither heat nor lack of water bring people such troubles as sandstorms.
A sure sign that dry winds are approaching (a dry wind is a dry hot wind that brings a prolonged drought) or a sandstorm is haze on the horizon. A little time will pass - and the daylight will grow dim: it will be covered with a muddy veil. But these are not clouds that bring blessed rain, but a canopy of the smallest dust raised by the winds.
Where dry winds and sandstorms have passed, plants fade, dry up and die. > - so people called these evil winds.
A sandstorm is a very terrible phenomenon, it is an element that raises tons of sand and dust into the air; they are common in arid and desert regions. The most famous African sandstorms in the Sahara.
The Sahara Desert is the largest desert on Earth covering an area of 9 million square kilometers in North Africa. This is one of the regions of the Earth with the most unfavorable living conditions. The air temperature often reaches 55 degrees, and the soil temperature - 80. Many thousands of people died in the sands of this desert. Entire caravans carrying slaves, ivory, gold or salt disappeared into the desert without a trace.
Another terrible phenomenon from sand is sand dunes (dunes are coastal sand hills, sediments moved by the wind). They are often found in deserts, but also occur on the sea coasts, on the shores of lakes. The movement of the dunes can lead to terrible consequences for people. Sand falls asleep forests, fields, roads, buildings and entire villages. To stop the sand, various measures are used: plantings, mechanical barriers.
In some places you can find petrified dunes. Sometimes this indicates that in the past there was a desert in this place. In many places on the globe people have lived in fear of quicksand for centuries. They were credited with the mysterious ability to suck in the victim until there was not a trace of it left on the surface of the earth.
Quicksand is sand with very fine grains of sand containing large amounts of water. Unlike ordinary sand grains, which have an irregular or pointed shape, quicksand sand grains are small round balls. Heavy objects here very easily disappear from the surface, as if sucked in by sand. Unlike ordinary quicksand not at all flexible. Therefore, walking on them is extremely dangerous - you can simply >.
What is quicksand, or, as it is also called, quicksand?
It is light, loose sand with a high water content. In appearance, it does not differ in any way from the ordinary sand that is next to it. However, there is still a difference between them: quicksand is not a support for heavy things.
Most often, quicksand is found in marshy places, on the shores of the seas, in the mouths of rivers.
People caught in quicksand can be saved. Since they contain a lot of moisture, they can swim just like in water. You just need to remember that once in them you need to move slowly enough. This allows the sand to flow around your body, as it does when you swim in water. In this case, you can save your life.
If sand is so dangerous, then: How do plants and animals manage to live in the sand? There are many different types of deserts. In some, there is a scorching heat all year, from which even the sand groans. In others, hot summers are replaced by very cold winters. In each of the deserts, only special species of animals and plants can exist. Shrub plants living in deserts have very small leaves, or none at all. Small leaf surface prevents evaporation too a large number moisture from the plant. Mexican cacti, for example, have thick, fleshy stems and spines instead of true leaves. Many plants have thorns and needles, while others have an unpleasant taste and smell. Thus, they protect themselves from animals and do not allow themselves to be eaten.
Animals that live among the sands, without exception, are able to do without water for a long time and get to sources that are at a great distance from each other. by the most best example the desert dweller is the camel. He has special pads on his feet to make it easier to walk on hot sand, a stomach in which water accumulates, a fatty hump - an energy reserve needed during long transitions, and tightly closed nostrils that prevent sand from entering the lungs during sandstorms.
Many of the little desert dwellers do not drink water at all. They get moisture from plant sap and night dew on leaves and stones.
People came up with the idea of growing watermelons in deserts. Yes, I was not mistaken, it was watermelons. Yes, and they grow large, up to 10 - 12 kilograms. There are melon watermelons, which we all know, but there are also dry watermelons: very sweet, with a salty aftertaste. How do you manage to grow them among the sea of sand, without watering, under the scorching sun?
This is done simply. In early spring, the nomad goes to rake the sand next to the saxaul or camel thorn. The inhabitant of the sands knows that the roots of desert plants go far into the depths, where there is water, salts, and the coolness necessary for all living things.
It is necessary to tear the ground up to about an elbow, make an incision on the root of a saxaul or a thorn and carefully insert a watermelon seed into it. It is from it that openwork lashes will then grow, the watermelon root will grow together with the saxaul and will receive the same moisture as it>. In autumn, large ripe watermelons will definitely grow here. Walking on such plantations should be done with caution. From any noise, even from a loud voice, a watermelon can crack. This cannot be allowed. Watermelon should make a crunch only at the touch of a sharp knife. This is an unshakable rule of desert nomads.
Why does a person need sand? Sand is indispensable in construction. Sand is a filler for concrete, reinforced concrete, ballast for railways and roads, a material for earthen dams and dams. It turns out that we live among the sand, we also walk and drive on the sand, but that's not all. If you look out the window through the glass, then we can see everything that is behind it, but it turns out that the glass is made of pure quartz sand and the necessary additives. Heat-resistant chemical utensils, crystal products and much more are also made from quartz sand.
But that's not all. Since ancient times, people have admired the beauty of pearls. Pearls were considered an adornment only for the rich. The ancient Indians believed that pearls are formed in the shell from the fact that dew drops fall into it. Similar legends were spread both in China and in Russia. In fact, everything happens differently. The beginning of a pearl is given by a grain of sand that has fallen between the inner surface of the shell and the mantle. The oyster covers this grain of sand with mother-of-pearl layer by layer. As a result, after some time, a shiny ball is formed. This is the pearl.
Sand and people
And people are very fond of traveling, admiring the famous sands.
And some people are attracted to the rally on the sands.
Creativity from sand
Sand is a short-lived material, but it attracts people to itself and makes them create.
Beauty at the festival > fascinates and delights everyone.
Now more and more people are addicted >.
And you can also visit the sand museums to listen to the sounds.
Sounds in the desert.
The song of the sands, the song of the sirens, luring travelers to certain death in the waterless desert, bell ringing monasteries buried in the depths of the sands.
This is how the English researcher R. A. Bagnould, the author of the first book on singing sands, published in 1954, describes his impressions. Nomads who heard these mysterious sounds considered them to be the voices of ghosts and demons living in sand dunes. And although today it is known that acoustic vibrations arise as a result of the movement of sand layers, this phenomenon has not yet been fully explained. There are two types of sounding sands - "humming" and "whistling", which differ in the frequency and duration of the emitted sound, as well as the conditions necessary for its occurrence.
The most common are "whistling" or "squeaking" sands, so named because of their ability to produce short, lasting less than a quarter of a second, high-frequency sounds - from 500 to 2500 Hz. Walking on such sand, you can hear a slight whistle under your feet. The sound is musically pure and may contain five or six harmonic overtones. There are whistling sands on sea coasts, on the banks of rivers and lakes around the world. "Buzzing" sands are considered to be a rarer and more unique phenomenon. You can hear them only deep in the desert near individual large dunes. Falling down in avalanches, such sands emit a loud low-frequency sound (50-300 Hz), usually lasting a few seconds, but sometimes up to 15 minutes. Sound can be so strong that it travels 10 kilometers, and is often accompanied by vibrations of the soil (seismic tremors), many times more intense than sound vibrations. Unlike whistles, the sound of humming dunes, in addition to the main frequency, contains many close frequencies. At the same time, more than one harmonic of the fundamental tone never occurs. For centuries, this "rumble" caused superstitious horror among the inhabitants of the desert, giving rise to a lot of legends and tales. So, Marco Polo in 1295 wrote about the evil spirits of the desert, which "at times fill the air with the sounds of all kinds of musical instruments, beat drums and clap their hands." The sound of humming sands sometimes resembles a drum roll, sometimes the sounds of a trumpet, harp and even bells. Today it is often compared to the buzz of telegraph wires or the propellers of a low-flying aircraft. More than 30 humming dunes are currently known in North and South America, Africa, Asia, the Arabian Peninsula and Hawaiian Islands. But to hear the humming sands, it is not necessary to travel to distant lands. You need to have a computer with a sound card and Internet access. Desert Songs are available at http://www. yo. rim. or. jp/~smiwa/sound/badaja. html. The fact that whistling sands are found mainly on the coasts, and buzzing sands - only deep in deserts, is apparently due to their different response to moisture. In order for the sand to "buzz", at least several weeks of drought are necessary: the grains of sand must be absolutely dry. Even with low atmospheric humidity, a thin film of water forms on their surface, preventing sound, and five drops of water can silence a whole liter of buzzing sand. Whistling also occurs only in dry sand. However, for the best sound, it is simply necessary to periodically wash the whistling sand with water. Sometimes with its help it is even possible to "revive" the sand, which for some reason has lost its ability to make sounds. Perhaps this is due to the fact that water washes out pollution from the sand, and it becomes looser. In any case, whistling sands rarely extend more than 30 meters inland.
Currently, the number of sounding sands on our planet is rapidly declining. This is due to heavy traffic on the coasts and in deserts, with the development of mass tourism, air and water pollution. It can be said that the musical abilities of the sands serve as a natural indicator of the ecological state of the Earth. Protection of the unique natural phenomenon from complete destruction requires special measures. To this end, on November 17, 1994, the World Singing Sands Symposium was convened in Nima, Japan. It discussed the tasks of preserving and reviving the sounding sands on the basis of international cooperation and a scientific approach to the problem. The center of the movement to protect the singing sands from destruction was the Japanese city of Nima. On March 3, 1991, the Sand Museum was opened there, where unique collections of sands from all over the world are collected. This museum is famous for the fact that it houses the world's largest hourglass: five meters high and a meter in diameter. During the whole year, a ton of sand is poured from the upper reservoir of the watch to the lower one. On the last day of every year, exactly at midnight, locals gently turn over this giant sand calendar - and everything starts again.
