INSTRUCTIONS TO WORK ON THE VIDEO :

Deep beneath the geysers and hot springs of Yellowstone Caldera lies a magma chamber produced by a hot spot in the earth’s mantle. As the magma moves towards the Earth’s surface, it crystallizes to form young, hot igneous rocks. The heat from these rocks drives groundwater towards the surface. As the water cools, ions precipitate out as mineral crystals, including quartz crystals from silicon and oxygen, feldspar from potassium, aluminum, silicon, and oxygen, galena from lead and sulfur.

Many of these crystals have signature shapes— take this cascade of pointed quartz, or this pile of galena cubes. But what causes them to grow into these shapes again and again? 

Part of the answer lies in their atoms. Every crystal’s atoms are arranged in a highly organized, repeating pattern. This pattern is the defining feature of a crystal, and isn’t restricted to minerals— sand, ice, sugar, chocolate, ceramics, metals, DNA, and even some liquids have crystalline structures. 

Each crystalline material’s atomic arrangement falls into one of six different families: cubic, tetragonal, orthorhombic, monoclinic, triclinic, and hexagonal. Given the appropriate conditions, crystals will grow into geometric shapes that reflect the arrangement of their atoms. Take galena, which has a cubic structure composed of lead and sulfur atoms. The relatively large lead atoms are arranged in a three-dimensional grid 90 degrees from one another, while the relatively small sulfur atoms fit neatly between them. As the crystal grows, locations like these attract sulfur atoms, while lead will tend to bond to these places. Eventually, they will complete the grid of bonded atoms. This means the 90 degree grid pattern of galena’s crystalline structure is reflected in the visible shape of the crystal. 

Quartz, meanwhile, has a hexagonal crystalline structure. This means that on one plane its atoms are arranged in hexagons. In three dimensions, these hexagons are composed of many interlocking pyramids made up of one silicon atom and four oxygen atoms. So the signature shape of a quartz crystal is a six-sided column with pointed tips. 

Depending on environmental conditions, most crystals have the potential to form multiple geometric shapes. For example, diamonds, which form deep in the Earth’s mantle, have a cubic crystalline structure and can grow into either cubes or octahedrons. Which shape a particular diamond grows into depends on the conditions where it grows, including pressure, temperature, and chemical environment. While we can’t directly observe growth conditions in the mantle, laboratory experiments have shown some evidence that diamonds tend to grow into cubes at lower temperatures and octahedrons at higher temperatures. Trace amounts of water, silicon, germanium, or magnesium might also influence a diamond’s shape. And diamonds never naturally grow into the shapes found in jewelry— those diamonds have been cut to showcase sparkle and clarity. 

Environmental conditions can also influence whether crystals form at all. Glass is made of melted quartz sand, but it isn’t crystalline. That’s because glass cools relatively quickly, and the atoms do not have time to arrange themselves into the ordered structure of a quartz crystal. Instead, the random arrangement of the atoms in the melted glass is locked in upon cooling. 

Many crystals don’t form geometric shapes because they grow in extremely close quarters with other crystals. Rocks like granite are full of crystals, but none have recognizable shapes. As magma cools and solidifies, many minerals within it crystallize at the same time and quickly run out of space. And certain crystals, like turquoise, don’t grow into any discernible geometric shape in most environmental conditions, even given adequate space. 

Every crystal’s atomic structure has unique properties, and while these properties may not have any bearing on human emotional needs, they do have powerful applications in materials science and medicine. 

According to the video, are these statements true or false?

1. The formation of crystals derives partly from the arrival of magma at the surface.
2. Crystals composed by the same atoms have the same shapes.
3. The surroundings where the crystals are formed can sometimes influence their shapes.
4. Crystals always have their shapes reworked before being sold.
5. Glass decreases its temperature at slow speed, that is why it never acquires a crystal form.
6. Crystals always have geometrical forms.
7. Crystals please human emotional needs.

1. T
2. F
3. F
4. T
5. F
6. F
7. F

Please take a look at the following sentence from the text:

As the crystal grows, locations like these attract sulfur atoms, while lead will tend to bond to these places. 

Can you tell me what function does as and while have in the sentence?

Answer: They both have a time function. They are transmitting an idea that occurs at the same time.

In order to connect sentences and join the ideas, we use the connectors of speech. They give coherence to the text and help the speech to sound more fluent.

Try to complete the exercise below with the given connectors:

Unless, even if, otherwise, so that, whereas

1. ____________ you saved a lot, you wouldn't be able to afford that house.
2. He eats only healthy food ____________  his sister gorges herself with junk food.
3. You should learn more,  ____________  you might fail your exams.
4. I cooked dinner ____________  my friends wouldn't have to eat out.
5. ____________  we're at the bus station by seven o'clock, we'll miss our bus.

1. Even if
2. whereas
3. otherwise
4. so that
5. unless

Traduire les phrases suivantes en anglais, issues du texte, puis retrouver ces phrases dans les deux premiers paragraphes du texte en anglais:

1.La chaleur de ces roches pour les eaux souterraines vers la surface.

.

2. Mais pourquoi si forment-t-ils toujours selon la même forme encore et encore?

Essential Grammar in use p 165-166

Unit 79  Every and All

Complete with every day or all day.

1. Yesterday it rained ........
2. I buy a newspaper ............ but sometimes I don't read it.
3. I'm not going out tomorrow. I'll be home .....
4. I usually drink four cups of coffee ............
5. Paula was ill yesterday, so she stayed in bed ............
6. Last year we went to the seaside for a week and it rained .........
7. I'm tired now because I've been working hard ...........

1. all day
2. every day
3. all day
4. every day
5. all day
6. every day
7. all day

(please note that this definitions are according to the context)

Geysers (noun, plural of geyser) - a hole in the ground from which hot water

and steam come out.

Mantle (noun) - the part of the earth that surrounds the central core.

Igneous (adjective) - describes rocks made from magma that have cooled and became solid.

Take (this cascade) (verb to take) - consider for example (...).

Lead (noun) - a chemical element that is a very heavy, soft, dark grey, poisonous metal.

Grid (noun) - a pattern or structure made from horizontal and vertical lines crossing each other to form squares.

Interlocking (adjective) - firmly joined together.

Showcase (verb) - exhibit; display.

Discernible (adjective) - able to be seen, recognized, or understood.

Have any bearing on (expression) - not relevant to something, no influence on.

Peseshet is a doctor and a teacher. The video describes a typical day of her life.

Now it is you turn. Write a text :

- Present yourself.

- Describe your profession.

- Tell what you did to get this job.

- Describe a typical day of your life : what usually happens when you are at work?

You can book a one to one class with a teacher who will correct your writing exercise.  One to one classes can be online, with a video call, anytime of the day. 

This gives you full flexibility for your timetable.

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