Freezing rain is the name given to rain maintained at temperatures below freezing by the ambient air mass that causes freezing on contact with surfaces. Unlike a mixture of rain and snow, ice pellets, or hail, freezing rain is made of liquid droplets; the raindrops become supercooled while passing through a sub-freezing layer of air hundreds of meters above the ground, freeze upon impact with any surface they encounter, including the ground, electrical wires and automobiles. The resulting ice, called glaze ice, can accumulate to a thickness of several centimeters and cover all exposed surfaces; the METAR code for freezing rain is FZRA. A storm that produces a significant thickness of glaze ice from freezing rain is referred to as an ice storm. Although these storms are not violent, freezing rain is notorious for causing travel problems on roadways, breaking tree limbs, downing power lines from the weight of accumulating ice. Downed power lines cause power outages in affected areas while accumulated ice can pose significant overhead hazards.
It is known for being dangerous to aircraft since the ice can effectively'remould' the shape of the airfoil and flight control surfaces. Freezing rain is associated with the approach of a warm front, when subfreezing air is trapped in the lowest levels of the atmosphere while warm air advects in aloft; this happens, for instance, when a low pressure system moves from the Mississippi River Valley toward the Appalachian Mountains and the Saint Lawrence River Valley of North America during the cold season, with a strong high pressure system sitting further east. This setup is known as cold-air damming, is characterized by cold and dry air at the surface within the region of high pressure; the warm air from the Gulf of Mexico is the fuel for freezing precipitation. Freezing rain develops when falling snow encounters a layer of warm air aloft around the 800 mbar level, causing the snow to melt and become rain; as the rain continues to fall, it passes through a layer of subfreezing air just above the surface and cools to a temperature below freezing.
If this layer of subfreezing air is sufficiently deep, the raindrops may have time to freeze into ice pellets before reaching the ground. However, if the subfreezing layer of air at the surface is shallow, the rain drops falling through it will not have time to freeze and they will hit the ground as supercooled rain; when these supercooled drops make contact with the ground, power lines, tree branches, aircraft, or anything else below 0 °C, a portion of the drops freezes, forming a thin film of ice, hence freezing rain. The specific physical process by which this occurs is called nucleation. Surface observations by manned or automatic stations are the only direct confirmation of freezing rain. One can never see directly freezing rain or snow on weather radars, Doppler or conventional. However, it is possible to estimate the area covered by freezing rain with radars indirectly; the intensity of the radar echoes is proportional to the form of its diameter. In fact, rain has much stronger reflective power than snow but its diameter is much smaller.
So the reflectivity of rain coming from melted snow is only higher. However, in the layer where the snow is melting, the wet flakes still have a large diameter and are coated with water so the returns to the radar is much stronger; the presence of this brightband indicates. This could be producing rain on the ground or the possibility of freezing rain if the temperature is below freezing; this artifact can be located, with a cross-section through radar data. The height and slope of the brightband will give clues to the extent of the region where melting occurs, it is possible to associate this clue with surface observations and numerical models prediction to produce output such as the ones seen on television weather programs that divide radar echoes into rain and snow precipitations. Freezing rain causes major power outages by forming glaze ice; when the freezing rain or drizzle is light and not prolonged, the ice formed is thin and causes only minor damage. When large quantities accumulate, however, it is one of the most dangerous types of winter hazard.
When the ice layer exceeds 6.4 mm, tree limbs with branches coated in ice can break off under the enormous weight and fall onto power lines. Windy conditions and lightning, when present, will exacerbate the damage. Power lines coated with ice become heavy, causing support poles and lines to break; the ice that forms on roadways makes vehicle travel dangerous. Unlike snow, wet ice provides no traction, vehicles will slide on gentle slopes; because freezing rain does not hit the ground as an ice pellet but still as a rain droplet, it conforms to the shape of the ground, or object such as a tree branch or car. This makes one thick layer of ice called "glaze". Freezing rain and glaze ice on a large scale is called an ice storm. Effects on plants can be severe. Trees may snap as they are fragile during winter weather. Pine trees are victims of ice storms as their needles will catch the ice, but not be able to support the weight. In February 1994, a severe ice storm caused over $1 billion in damage in the Southern United States in Mississippi, Tennessee and Western North Carolina the
Cumulus clouds are clouds which have flat bases and are described as "puffy", "cotton-like" or "fluffy" in appearance. Their name derives from the Latin cumulo -, meaning pile. Cumulus clouds are low-level clouds less than 2,000 m in altitude unless they are the more vertical cumulus congestus form. Cumulus clouds may appear in lines, or in clusters. Cumulus clouds are precursors of other types of clouds, such as cumulonimbus, when influenced by weather factors such as instability and temperature gradient. Cumulus clouds produce little or no precipitation, but they can grow into the precipitation-bearing congestus or cumulonimbus clouds. Cumulus clouds can be formed from water vapor, supercooled water droplets, or ice crystals, depending upon the ambient temperature, they come in many distinct subforms, cool the earth by reflecting the incoming solar radiation. Cumulus clouds are part of the larger category of free-convective cumuliform clouds, which include cumulonimbus clouds; the latter genus-type is sometimes categorized separately as cumulonimbiform due to its more complex structure that includes a cirriform or anvil top.
There are cumuliform clouds of limited convection that comprise stratocumulus and cirrocumulus. These last three genus-types are sometimes classified separately as stratocumuliform. Cumulus clouds form via atmospheric convection; as the air rises, the temperature drops. If convection reaches a certain level the RH reaches one hundred percent, the "wet-adiabatic" phase begins. At this point a positive feedback ensues: since the RH is above 100%, water vapor condenses, releasing latent heat, warming the air and spurring further convection. In this phase, water vapor condenses on various nuclei present in the air, forming the cumulus cloud; this creates the characteristic flat-bottomed puffy shape associated with cumulus clouds. The height of the cloud depends on the temperature profile of the atmosphere and the presence of any inversions. During the convection, surrounding air is entrained with the thermal and the total mass of the ascending air increases. Rain forms in a cumulus cloud via a process involving two non-discrete stages.
The first stage occurs. Langmuir writes that surface tension in the water droplets provides a higher pressure on the droplet, raising the vapor pressure by a small amount; the increased pressure results in those droplets evaporating and the resulting water vapor condensing on the larger droplets. Due to the small size of the evaporating water droplets, this process becomes meaningless after the larger droplets have grown to around 20 to 30 micrometres, the second stage takes over. In the accretion phase, the raindrop begins to fall, other droplets collide and combine with it to increase the size of the raindrop. Langmuir was able to develop a formula which predicted that the droplet radius would grow unboundedly within a discrete time period; the liquid water density within a cumulus cloud has been found to change with height above the cloud base rather than being constant throughout the cloud. At the cloud base, the concentration was 0 grams of liquid water per kilogram of air; as altitude increased, the concentration increased to the maximum concentration near the middle of the cloud.
The maximum concentration was found to be anything up to 1.25 grams of water per kilogram of air. The concentration dropped off as altitude increased to the height of the top of the cloud, where it dropped to zero again. Cumulus clouds can form in lines stretching over 480 kilometres long called cloud streets; these cloud streets may be broken or continuous. They form when wind shear causes horizontal circulation in the atmosphere, producing the long, tubular cloud streets, they form during high-pressure systems, such as after a cold front. The height at which the cloud forms depends on the amount of moisture in the thermal that forms the cloud. Humid air will result in a lower cloud base. In temperate areas, the base of the cumulus clouds is below 550 metres above ground level, but it can range up to 2,400 metres in altitude. In arid and mountainous areas, the cloud base can be in excess of 6,100 metres. Cumulus clouds can be composed of ice crystals, water droplets, supercooled water droplets, or a mixture of them.
The water droplets form when water vapor condenses on the nuclei, they may coalesce into larger and larger droplets. In temperate regions, the cloud bases studied ranged from 500 to 1,500 metres above ground level; these clouds were above 25 °C, the concentration of droplets ranged from 23 to 1300 droplets per cubic centimeter. This data was taken from growing isolated cumulus clouds; the droplets were small, ranging down to around 5 micrometers in diameter. Although smaller droplets may have been present, the measurements were not sensitive enough to detect them; the smallest droplets were found in the lower portions of the clouds, with the percentage of large droplets rising in the upper regions of the cloud. The droplet size distribution was bimodal in nature, with peaks at the small and large droplet sizes and a slight trough in the intermediate size range; the skew was neutral. Furthermore, large droplet size is inversely proporti
Pumpable ice technology
Pumpable ice technology is a technology to produce and use fluids or secondary refrigerants called coolants, with the viscosity of water or jelly and the cooling capacity of ice. Pumpable ice is a slurry of ice crystals or particles ranging from 5 to 10,000 micrometers in diameter and transported in brine, food liquid, or gas bubbles of air, ozone, or carbon dioxide. Besides generic terms such as pumpable, jelly or slurry ice, there are many trademark names for such coolant, like "Deepchill", “Beluga”, “optim”, “flow”, “fluid”, “jel”, “binary”, “liquid”, “maxim”, “whipped”, “bubble slurry” ice; these trademarks are authorized by industrial ice maker production companies in Australia, China, Iceland, Russia, United Kingdom, USA. There are two simple methods for producing pumpable ice; the first is to manufacture used forms of crystal solid ice, such as plate, shell or flake ice, by crushing and mixing it with water. This mixture of different ice concentrations and particle dimensions is passed by pumps from a storage tank to the consumer.
The constructions and applications of current conventional ice makers are described in. The idea behind the second method is to create the crystallization process inside of the volume of the cooled liquid; this crystallization inside can be accomplished using cooling technologies. In vacuum technology low pressure forces a small part of the water to evaporate while the remaining water freezes forming a water-ice mixture. Depending on the additive concentrations, the final temperature of pumpable ice is between zero and –4 °C; the large volume of vapor and an operating pressure of about 6 mbar require the use of a water vapor compressor with a great swept volume. This technology is economically reasonable and can be recommended for systems with cooling capacity of 1 MW or larger. Crystallization by cooling can be done using indirect systems. A refrigerant is directly injected inside the liquidThe advantage of this method is the absence of any intermediate device between the refrigerant and the liquid.
However, the absence of heat loss between refrigerant and liquid in the process of thermal interaction may cause problems. The safety measures that have to be implemented, the need for the additional step of refrigerant separation, difficulties in producing crystals are further disadvantages of this method. In indirect methods the evaporator is assembled either horizontally or vertically, it has a shell tubing assembled with one to a hundred inner tubes and containing a refrigerant that evaporates between the shell and the internal tubing. Liquid flows through the tubing of the small diameter. In the inside volume of the evaporator cooling, super cooling and freezing of liquid take place due to heat exchange with the crystallizer-cooled wall; the idea is to use a well-polished evaporator surface and appropriate mechanisms to prevent tubing from adhering to the ice embryos, to prevent growth and a thickening of the ice on the inside cooling surface. A whip rod, a screw or a shaft with metallic or plastic wipers is used as a mechanism for removal.
Indirect pumpable ice technologies produce pumpable ice consisting of 5 to 50 micrometer crystals and have a number of advantages. They can produce 1,000 kg of crystal ice at the low energy expenditure of 60 to 75 kWh instead of the 90 to 130 kWh required to produce regular water ice. Further improvements are expected to lead to a specific energy expenditure for ice production of 40 to 55 kWh per 1,000 kg of pure ice and a high specific ice capacity per an area value at the evaporator cooling surface. Commercial evaporators of the double-pipe type used in the food and fish industries have an inside diameter of interior tube and length in a range of 50–125 mm and 60–300 cm. For the dewaxing lubrication oil, evaporators are used with the following dimensions: internal diameter of the inner tube is 150–300 mm. Sometimes a gas can be added to the liquid flowing through the evaporator, it destroys a liquid laminar layer on the cooled surface of the heat exchanger-crystallizer, increases flow turbulence, decreases the average viscosity of pumpable ice.
Different liquids, such as sea water, brines, or glycol solutions of additives with more than 3–5% concentrations and a freezing point less than −2 °C are used in the process. The equipment for the production and supplying of pumpable ice includes an ice maker, a storage tank, a heat exchanger, piping and electrical and electronic appliances and devices. Pumpable ice with maximum ice concentration of 40% can be pumped straight from the ice maker to the consumer; the final possible ice concentration of pumpable ice in the storage tank is 50%. The maximum value of cooling energy of pumpable ice accumulated in the storage tank in a homogeneous phase is about 700 kWh, which corresponds to 10–15 m3 volume of a storage tank. A high-shear mixer is used to prevent the separation of ice from the cooled liquid and keeps the ice concentration unchanged over time and unaffected by the tank height. Pumpable ice is transported from the storage tank to a place of consumption that could be hundreds of meters away.
The practical ratio between the required electric power of the submersible mixer motor and the “kneaded” pumpable ice volume is 1:1. In the tanks with volumes larger than 15 m3, pumpable ice is not mixed and the cold energy of stored ice is only used by a heat transfer of liquid that
Refrigeration is a process of removing heat from a low-temperature reservoir and transferring it to a high-temperature reservoir. The work of heat transfer is traditionally driven by mechanical means, but can be driven by heat, electricity, laser, or other means. Refrigeration has many applications, but not limited to: household refrigerators, industrial freezers and air conditioning. Heat pumps may use the heat output of the refrigeration process, may be designed to be reversible, but are otherwise similar to air conditioning units. Refrigeration has had a large impact on industry, lifestyle and settlement patterns; the idea of preserving food dates back to at least Chinese empires. However, mechanical refrigeration technology has evolved in the last century, from ice harvesting to temperature-controlled rail cars; the introduction of refrigerated rail cars contributed to the westward expansion of the United States, allowing settlement in areas that were not on main transport channels such as rivers, harbors, or valley trails.
Settlements were developing in infertile parts of the country, filled with newly discovered natural resources. These new settlement patterns sparked the building of large cities which are able to thrive in areas that were otherwise thought to be inhospitable, such as Houston and Las Vegas, Nevada. In most developed countries, cities are dependent upon refrigeration in supermarkets, in order to obtain their food for daily consumption; the increase in food sources has led to a larger concentration of agricultural sales coming from a smaller percentage of existing farms. Farms today have a much larger output per person in comparison to the late 1800s; this has resulted in new food sources available to entire populations, which has had a large impact on the nutrition of society. As quite similar criteria shall be fulfilled by working fluids applied to heat pumps, refrigeration and ORC cycles, several working fluids are applied by all these technologies. Ammonia was one of the first refrigerants. Refrigeration can be defined as "The science of providing and maintaining temperature below that of surrounding atmosphere".
It means continuous extraction of heat from a body whose temperature is below the temperature of its surroundings. The seasonal harvesting of snow and ice is an ancient practice estimated to have begun earlier than 1000 BC. A Chinese collection of lyrics from this time period known as the Shijing, describes religious ceremonies for filling and emptying ice cellars. However, little is known about the construction of these ice cellars; the next ancient society to harvest ice may have been the Jews according to the book of Proverbs, which reads, “As the cold of snow in the time of harvest, so is a faithful messenger to them who sent him.” Historians have interpreted this to mean that the Jews used ice to cool beverages rather than to preserve food. Other ancient cultures such as the Greeks and the Romans dug large snow pits insulated with grass, chaff, or branches of trees as cold storage. Like the Jews, the Greeks and Romans did not use ice and snow to preserve food, but as a means to cool beverages.
The Egyptians developed methods to cool beverages, but in lieu of using ice to cool water, the Egyptians cooled water by putting boiling water in shallow earthen jars and placing them on the roofs of their houses at night. Slaves would moisten the outside of the jars and the resulting evaporation would cool the water; the ancient people of India used this same concept to produce ice. The Persians stored ice in a pit called a Yakhchal and may have been the first group of people to use cold storage to preserve food. In the Australian outback before a reliable electricity supply was available where the weather could be hot and dry, many farmers used a "Coolgardie safe"; this consisted of a room with hessian "curtains" hanging from the ceiling soaked in water. The water would evaporate and thereby cool the hessian curtains and thereby the air circulating in the room; this would allow many perishables such as fruit and cured meats to be kept that would spoil in the heat. Before 1830, few Americans used ice to refrigerate foods due to a lack of ice-storehouses and iceboxes.
As these two things became more available, individuals used axes and saws to harvest ice for their storehouses. This method proved to be difficult and did not resemble anything that could be duplicated on a commercial scale. Despite the difficulties of harvesting ice, Frederic Tudor thought that he could capitalize on this new commodity by harvesting ice in New England and shipping it to the Caribbean islands as well as the southern states. In the beginning, Tudor lost thousands of dollars, but turned a profit as he constructed icehouses in Charleston, Virginia and in the Cuban port town of Havana; these icehouses as well as better insulated ships helped reduce ice wastage from 66% to 8%. This efficiency gain influenced Tudor to expand his ice market to other towns with icehouses such as New Orleans and Savannah; this ice market further expanded as harvesting ice became faster and cheaper after one of Tudor’s suppliers, Nathaniel Wyeth, invented a horse-drawn ice cutter in 1825. This invention as well as Tudor’s success inspired others to get involved in the ice trade and the ice industry grew.
Ice became a mass-market commodity by the early 1830s with the price of ice dropping from six cents per pound to a half of a cent per pound. In New York City, ice consumption increased from 12,000 tons in 1843 to 100,000 tons in 1856. Boston’s consumption leapt from 6,000 tons to 85,000 tons during that same period. Ice harvesting created a “cooling cultur
A spruce is a tree of the genus Picea, a genus of about 35 species of coniferous evergreen trees in the family Pinaceae, found in the northern temperate and boreal regions of the Earth. Spruces are large trees, from about 20–60 m tall when mature, have whorled branches and conical form, they can be distinguished from other members of the pine family by their needles, which are four-sided and attached singly to small persistent peg-like structures on the branches, by their cones, which hang downwards after they are pollinated. The needles are shed. In other similar genera, the branches are smooth. Spruce are used as food plants by the larvae of some Lepidoptera species, such as the eastern spruce budworm, they are used by the larvae of gall adelgids. In the mountains of western Sweden, scientists have found a Norway spruce, nicknamed Old Tjikko, which by reproducing through layering, has reached an age of 9,550 years and is claimed to be the world's oldest known living tree; the word spruce comes from a Middle English adjective spruse which meant from Prussia.
The adjective comes from an unknown alteration of an Old French form of Prussia - Pruce, which itself comes from New Latin, which adapted it from Old Prussian. Spruce and Sprws seem to have been generic terms for commodities brought to England by Hanseatic merchants, the tree thus was believed to be particular to Prussia, which for a time was figurative in England as a land of luxuries. DNA analyses have shown that traditional classifications based on the morphology of needle and cone are artificial. A recent study found that P. breweriana had a basal position, followed by P. sitchensis, the other species were further divided into three clades, suggesting that Picea originated in North America. Spruce has been found in the fossil record from the early Cretaceous, 136 million years ago. Thirty-five named species of spruce exist in the world; the Plant List has 59 accepted spruce names. Basal species: Picea breweriana – Brewer's spruce, Klamath Mountains, North America. Beyond that, determination can become more difficult.
Intensive sampling in the Smithers/Hazelton/Houston area of British Columbia showed Douglas, according to Coates et al. that cone scale morphology was the feature most useful in differentiating species of spruce. Daubenmire, after range-wide sampling, had recognized the importance of the 2 latter characters. Taylor had noted that the most obvious morphological difference
Sprite is a colorless, caffeine-free and lime-flavored soft drink created by The Coca-Cola Company. It was first developed in West Germany in 1959 as Fanta Klare Zitrone and was introduced in the United States under the current brand name Sprite in 1961 as a competitor to 7 Up. Sprite advertising makes use of the portmanteau word lymon, a combination of the words "lemon" and "lime". By the 1980s, Sprite had developed a large following among teenagers. In response, Sprite began to cater to this demographic in their advertisements in 1987. "I Like the Sprite In You" was the brand's first long-running slogan, many jingles were produced around it before its discontinuation in 1994. In 1994, Sprite revamped their marketing logo, slogan, as well; the new, more vibrant logo stood out more on packaging, featured a blue-to-green gradient with silver "splashes" and subtle white "bubbles" in the background. The product name, "Sprite" had a blue backdrop shadow on the logo; the words. This logo was used in the United States until 2006, similar variants were used in other countries until this year as well.
The brand's slogan was changed to. One of the first lyrics for the new slogan were: "never forget yourself'cause first things first, grab a cold, cold can, obey your thirst.” Under the new slogan, Sprite tapped into hip-hop culture by leveraging up and coming, as well as underground rap artists including. Sprite expanded its urban connections in the late 1990s by featuring both amateur and accomplished basketball players in their advertisements. To this day, NBA players and hip-hop artists such as LeBron James, Vince Staples, Lil Yachty appear in Sprite adverts. In 1998, one commercial poked fun at products which featured cartoon mascots in the style of a horror film. In it, the mascot for a fictitious orange juice drink called "Sun Fizz" comes to life, terrifying the kids and mother, starts to chase them; this commercial is notorious for ending on a cliffhanger which still remains unresolved to this day. In the 1990s, one of Sprite's longest-running ad campaigns was "Grant Hill Drinks Sprite", in which the well-liked basketball player's abilities, Sprite's importance in giving him his abilities, were humorously exaggerated.
In 2000, Sprite commissioned graffiti artist Temper to design limited edition art, which appeared on 100 million cans across Europe. In 2004, Coke created Miles Thirst, a vinyl doll voiced by Reno Wilson, used in advertising to exploit the hip-hop market for soft drinks. In 2006, a new Sprite logo, consisting of two yellow and green "halves" forming an "S" lemon/lime design, made its debut on Sprite bottles and cans; the slogan was changed from its long running "Obey Your Thirst" to just "Obey" in the United States and was outright replaced with "Freedom From Thirst" in many countries. This was the decade's first major shift in advertising themes; the "Sublymonal" campaign was used as part of the alternate reality game the Lost Experience. This resurrected the "lymon" word. Sprite redesigned their label in 2009. In France in 2012, the drink was reformulated removing 30% of the sugar and replacing it with the sweetener Stevia; this led to the drink containing fewer calories. This soon spread to Ireland, the UK and the Netherlands in 2013.
A further formula change happened in the UK in 2018. This formula has less sugar than before. In Ireland in the same year, Sprite was relaunched and the Sprite Zero was renamed Sprite; the Sprite with sugar is no longer being sold. In addition, a version of the sugar free drink with Cucumber taste was added to the range. Soft drink Coca-Cola J-Hope Official website Sprite - Coca-ColaCompany.com
A crystal or crystalline solid is a solid material whose constituents are arranged in a ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macroscopic single crystals are identifiable by their geometrical shape, consisting of flat faces with specific, characteristic orientations; the scientific study of crystals and crystal formation is known as crystallography. The process of crystal formation via mechanisms of crystal growth is called crystallization or solidification; the word crystal derives from the Ancient Greek word κρύσταλλος, meaning both "ice" and "rock crystal", from κρύος, "icy cold, frost". Examples of large crystals include snowflakes and table salt. Most inorganic solids are not crystals but polycrystals, i.e. many microscopic crystals fused together into a single solid. Examples of polycrystals include most metals, rocks and ice. A third category of solids is amorphous solids, where the atoms have no periodic structure whatsoever.
Examples of amorphous solids include glass and many plastics. Despite the name, lead crystal, crystal glass, related products are not crystals, but rather types of glass, i.e. amorphous solids. Crystals are used in pseudoscientific practices such as crystal therapy, along with gemstones, are sometimes associated with spellwork in Wiccan beliefs and related religious movements; the scientific definition of a "crystal" is based on the microscopic arrangement of atoms inside it, called the crystal structure. A crystal is a solid where the atoms form a periodic arrangement.. Not all solids are crystals. For example, when liquid water starts freezing, the phase change begins with small ice crystals that grow until they fuse, forming a polycrystalline structure. In the final block of ice, each of the small crystals is a true crystal with a periodic arrangement of atoms, but the whole polycrystal does not have a periodic arrangement of atoms, because the periodic pattern is broken at the grain boundaries.
Most macroscopic inorganic solids are polycrystalline, including all metals, ice, etc. Solids that are neither crystalline nor polycrystalline, such as glass, are called amorphous solids called glassy, vitreous, or noncrystalline; these have no periodic order microscopically. There are distinct differences between crystalline solids and amorphous solids: most notably, the process of forming a glass does not release the latent heat of fusion, but forming a crystal does. A crystal structure is characterized by its unit cell, a small imaginary box containing one or more atoms in a specific spatial arrangement; the unit cells are stacked in three-dimensional space to form the crystal. The symmetry of a crystal is constrained by the requirement that the unit cells stack with no gaps. There are 219 possible crystal symmetries, called crystallographic space groups; these are grouped into 7 crystal systems, such as hexagonal crystal system. Crystals are recognized by their shape, consisting of flat faces with sharp angles.
These shape characteristics are not necessary for a crystal—a crystal is scientifically defined by its microscopic atomic arrangement, not its macroscopic shape—but the characteristic macroscopic shape is present and easy to see. Euhedral crystals are those with well-formed flat faces. Anhedral crystals do not because the crystal is one grain in a polycrystalline solid; the flat faces of a euhedral crystal are oriented in a specific way relative to the underlying atomic arrangement of the crystal: they are planes of low Miller index. This occurs; as a crystal grows, new atoms attach to the rougher and less stable parts of the surface, but less to the flat, stable surfaces. Therefore, the flat surfaces tend to grow larger and smoother, until the whole crystal surface consists of these plane surfaces. One of the oldest techniques in the science of crystallography consists of measuring the three-dimensional orientations of the faces of a crystal, using them to infer the underlying crystal symmetry.
A crystal's habit is its visible external shape. This is determined by the crystal structure, the specific crystal chemistry and bonding, the conditions under which the crystal formed. By volume and weight, the largest concentrations of crystals in the Earth are part of its solid bedrock. Crystals found in rocks range in size from a fraction of a millimetre to several centimetres across, although exceptionally large crystals are found; as of 1999, the world's largest known occurring crystal is a crystal of beryl from Malakialina, Madagascar, 18 m long and 3.5 m in diameter, weighing 380,000 kg. Some crystals have formed by magmatic and metamorphic processes, giving origin to large masses of crystalline rock; the vast majority of igneous rocks are formed from molten magma and the degree of crystallization depends on the conditions under which they solidified. Such rocks as granite, which have cooled slowly and under great pressures, have crystallized.