Category The World Around us

The speed at which glaciers move depends on the steepness of the slope, though they average a speed of around 2m (7ft) a day. It generally takes ice several thousand years to move from – one end of a glacier to the other.

The sheer weight of a thick layer of ice, or the force of gravity on the ice mass, causes glaciers to flow very slowly. Ice is a soft material, in comparison to rock, and is much more easily deformed by this relentless pressure of its own weight. Ice may flow down mountain valleys, fan out across plains, or in some locations, spread out onto the sea. Movement along the underside of a glacier is slower than movement at the top due to the friction created as it slides along the ground’s surface, and in some cases where the base of the glacier is very cold, the movement at the bottom can be a tiny fraction of the speed of flow at the surface.

Glaciers periodically retreat or advance, depending on the amount of snow accumulation or evaporation or melt that occurs. This retreat and advance refers only to the position of the terminus, or snout, of the glacier. Even as it retreats, the glacier still deforms and moves downslope, like a conveyor belt. For most glaciers, retreating and advancing are very slow occurrences, requiring years or decades to have a significant effect. However, when glaciers retreat rapidly, movement may be visible over a few months or years. For instance, massive glacier retreat has been recorded in Glacier Bay, Alaska. Glaciers that once terminated in the ocean have now receded onto land, retreating far up valleys. Over the past several decades, scientists and researchers have begun to capture data and photographic evidence of this recession over time.

Alternatively, glaciers may surge, racing forward several meters per day for weeks or even months. In 1986, the Hubbard Glacier in Alaska surged at the rate of 10 meters (32 feet) per day across the mouth of Russell Fjord. In only two months, the glacier had dammed water in the fjord and created a lake.

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Glaciation occurs when layers of snow build up in areas over a long period of time. The Layers become compressed and form a mass of ice. Where this happens in the valley areas of mountain range, the layers form into glaciers that, over rime, move slowly down the mountainside. In the Polar Regions, vast frozen areas known as ice caps are formed.

Glaciers are sheets of solidly packed ice and snow that cover large areas of land. They are formed in areas where the general temperature is usually below freezing. This can be near the North and South poles, and also on very high ground, such as large mountains. Snow upon snow on the land becomes compacted and turns into ice. Think about when you make a snowball. You gather fluffy snow in your hands and then press it together. The heat and pressure from your hands make some of the snow melt. When you take a hand away, the liquid water freezes again. The fluffy snow has been compacted into a hard snowball.

Glaciers are formed in a similar way, but on a much larger scale. Sunlight melts some of the snow. Then it freezes during the night, or if the temperature drops. More snow falls onto the surface. Eventually, the weight of snow layers upon snow layers, and the melting and freezing, turns the layers into solid ice. If this ice forms at a high elevation, it starts to slowly slip downhill as an ice “river.” It is called a glacier. On flat land this ice is called an ice cap.

Ice can change the surface of the land. When you look around you, you may not see snow or ice that lasts all year long. That’s what it takes to make a glacier. More snow must fall in a region in winter than melts in summer. When this happens, the amount of snow builds up over time. It’s a lot like money in the bank. If you put more in than you take out, your bank account will grow. Glaciers work the same way. When enough snow builds up in an area, the snow on the bottom becomes compacted by the weight above, changing it into ice. You may have simulated this when making an iceball out of snow or crushed ice.

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The hardness of minerals varies according to the structure of their atoms. A mineral’s hardness is measured using the Mohs scale. Diamond is the hardest mineral and thus has a rating of 10 Mohs.

It is difficult to distinguish between the hardness of a mineral and the ease with which a mineral may be broken. Hardness refers to the ability to scratch the mineral’s surface. However, some hard minerals, like diamond and quartz, break easily if dropped. Hence mineral breakage is different from hardness. Minerals break in two ways: fracture and cleavage. Fracture is irregular breakage. Cleavage is a regular breakage that follows the atomic structure of a mineral. Cleavage results in smooth, planar surfaces. Different minerals may have one, two, three, four, or six cleavages.

Mohs hardness scale is used by geologists to compare the hardness of minerals only. The scale arranges a series of minerals in order of increasing relative hardness, from 1 to 10. Note that this is a relative hardness scale; diamond is actually over four hundred times harder than talc.

PROCEDURE:

1. Draw the Mohs hardness scale on the board. Ask the students which of their lab samples are part of the scale. Ask them if they think the scale is useful. Tell them that the scale works well in a laboratory, but in the field, a geologist would not have all 10 minerals available. Geologists usually use their fingernails and steel knives.
    
2. Explain that the Mohs scale does not explain why some minerals are harder than others. Ask students to draw a large person that weighs 250 lbs. and a muscular person that weighs 250 lbs. Ask them if one person is “softer” than the other. One person works out more, and the cells of that body combine tightly, giving him or her a different appearance. The elements of some minerals do the same. The ones that are tightly bound together look different than do ones with looser bonds.

For example, in the illustrations below, (A) shows the atomic structure of carbon in a diamond, and (B) is the carbon arrangement in graphite. (A) is more compact than (B), hence it is harder. As an example, you can tell the students that when Superman squeezes a piece of carbon in his hand, it turns into a diamond. (Superman usually uses coal, which is not the right source of carbon, since the substance should be inorganic to be a real mineral.) If desired, have the students construct Googolplex models of graphite and diamond. Use the directions provided with the Googoplex models. You can also use the Zometool system to construct similar models.

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Pearls are precious stones formed inside shellfish such as oysters, mussels and clams. They form when a piece of grit enters the creature’s shell. The most valuable pearls are those from oysters.

Pearl is a valuable gem known to mankind since ancient times. The pearl, in fact, is of animal origin and produced by certain bivalves of Mollusca. The pearl producing bivalves are marine oysters of the genus Pinctada, though some freshwater bivalves of the genus Unio and Anodonta also produce pearl but of inferior quality and rarely of any use.

The pearl is secreted by the mantle as a protective measure against foreign objects like sand particles, parasites, small larvae or any object of organic and inorganic origin. In fact, as soon as a foreign object, somehow, enters the body of a bivalve in between the shell and mantle, the mantle immediately gets irritated and at once encloses it like a sac. The mantle wall then starts secreting layers of nacre around the foreign object from defence point of view.

Thus, mantle wall secretes continuously several layers of nacre around the foreign object and finally pearl is formed. The value of pearl depends upon its size, quality, etc. Now a day, the pearl producing bivalves are reared and pearls are produced artificially by introducing some foreign objects between the mantle and shell in the different parts of the world; Japan has surpassed all other countries in this field.

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Some minerals are very precious. Diamonds, rubies, emeralds and sapphires are examples of gemstones that are valued for their rarity and beauty. They are difficult to find and expensive to extract from the Earth. Some of them also have particular uses in science and industry that can increase their value.

Gemstones are beautiful pieces of nature that come from the earth that can be made into different types of jewelry. Gemstones are valuable: A lot of time, effort, and information go into mining gemstones. As time goes on, more and more natural gemstones are becoming rarer. As the cost of mining rises, these natural gemstones are harder to come by. Their value is constantly rising due to their scarcity, so one can make a profit from selling them as well.

There is a lot of information that goes into the grading process of all gemstones. First of all, the color of the stone will play a huge part in determining the grade of the stone. The things that matter when it comes to color are the saturation, the hue, the tint, the tone, the grade, the clarity, the brilliance, and several other factors. Other things that are involved in the evaluation of each gemstone include the price per carat, the size, the flaws within the stone, and whether or not the gemstone was mined or produced.

Gemstones are formed hundreds, thousands, and maybe even millions of year ago, so the gemstones that are available now are likely to be the only ones we have in this lifetime. Many mines around the world are empty because we have already gotten out the supply of gemstones available. Although many gemstones can be produced outside of Mother Nature’s gemstone mines, these are not as valuable as natural stones found in the earth. Unfortunately, it costs gemstone miners to do their jobs, and the cost of mining continues to escalate as the supply of the natural gemstones gets smaller and smaller: Miners have to go deeper and deeper into the earth’s surface in order to find these natural gemstones. This will cause gemstones to continue to grow in value as time goes on.

The rarer the stone is, the more it will continue to go up in value. Some of the more rare stones include opals, jade, colored diamonds, star rubies and star sapphires, cat’s eye (asterism) stones, topaz, emeralds, rubies, sapphires, tanzanite, and several others. Because these are rare gemstones, they are slightly more valuable. The larger the stone, the more valuable it will be as well.

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Crystals are formed from minerals that melt or are dissolved in liquids. Crystals in different types of rocks and minerals form one of six different geometric shapes. These shapes were discovered in the 18th century by Abbe Rene Flatly.

A crystal or crystalline solid is a solid material whose constituents, such as atoms, molecules or ions, are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macroscopic single crystals are usually 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 is derived from the Ancient Greek word (krustallos), meaning both “ice” and “rock crystal”, from (kruos), “icy cold, frost”.

Most minerals occur naturally as crystals. Every crystal has an orderly, internal pattern of atoms, with a distinctive way of locking new atoms into that pattern to repeat it again and again. The shape of the resulting crystal-such as a cube (like salt) or a six-sided form (like a snowflake)-mirrors the internal arrangement of the atoms. As crystals grow, differences in temperature and chemical composition cause fascinating variations. But students will rarely find in their backyard the perfectly shaped mineral crystals that they see in a museum. This is because in order to readily show their geometric form and flat surfaces, crystals need ideal growing conditions and room to grow. When many different crystals grow near each other, they mesh together to form a conglomerated mass. This is the case with most rocks, such as granite mentioned above, which is made up of many tiny mineral crystals. The museum-quality specimens shown in the images here grew in roomy environments that allowed the geometric shapes to form uninhibited.

The internal arrangement of atoms determines all the minerals’ chemical and physical properties, including color. Light interacts with different atoms to create different colors. Many minerals are colorless in their pure state; however, impurities of the atomic structure cause color. Quartz, for example, is normally colorless, but occurs in a range of colors from pink to brown to the deep purple of amethyst, depending on the number and type of impurities in its structure. In its colorless state, quartz resembles ice. In fact, the root for crystal comes from the Greek word krystallos-ice-because the ancient Greeks believed clear quartz was ice frozen so hard it could not melt.

CRYSTAL SHAPES

CUBIC                             Diamond is an example of a mineral with a cubic structure.

HEXAGONAL                 Beryl has a hexagonal crystal shape.

TETRAGONAL                Zircon has a tetragonal crystal structure.

MONOCLINIC               Gypsum has a monoclinic design.

ORTHOHOMBIC            Sulphur has an orthohombic crystal structure.

TRICLINIC                       Turquoise has crystals in a triclinic shape.

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