28. Changing of rocks

The rock cycle is a model of the continuous changing of rocks from one type to another. These changes, however, often take thousands of years, so it is impossible to trace a particular set of minerals through the cycle.

Igneous rocks are produced when magma cools. Magma that is forced to the surface as lava forms extrusive rocks. Magma that cools beneath Earth’s surface forms intrusive rocks.

Sedimentary rocks are characterized by their strata – layers that are formed out of mud, gravel, sand, bones, shells, and other animal matter. Most sedimentary rocks form in water. As layers settle on other layers, the layers beneath are compressed and become rock. This process is called compaction. When minerals dissolve in water and glue the materials together, the process is called cementation.

Metamorphic rocks form when already existing rocks are exposed to the tremendous heat and pressure present at or beneath Earth’s surface. When this happens, the materials in the rock can undergo both physical and chemical changes, depending on where and how the changes take place.

Exercises:

1. Answer the questions:

1. Why are the rocks changing?

2. What changes happen among different types of rocks?

2. Retell the text.

29. Rocks are made of minerals

The rocks are different. Some rocks are made of smaller parts. Some rocks are made of many different things.

Some of the things in the rocks are minerals. Minerals are solids that form naturally. They are not plants or animals. Minerals make a rock look and feel the way it does. They give rocks their different colors. They also make the rock hard or soft.

There are more than 3,000 kinds of minerals. They have different colors, hardnesses, and crystal shapes. Minerals are different because they are made of different materials. And they have their own structure inside. These are properties of minerals.

Where do you find minerals? Minerals can be found in rocks all around you. They are also found in the soil and in water. Minerals are even in plants and animals. You may eat a cereal with minerals added to it for breakfast. Living things need minerals to live and grow.

Notes:

hardness – твердість

luster – блиск, лоск

density – густота, щільність

magnetite – магнетит, магнітний залізняк.

fluorite – плавиковий шпат, флюоріт

Exercises:

1. Answer the questions:

1. What kinds of rocks do you know?

2. If you were to look for a special rock, what color would it be?

3. What would it smell and feel like?

4. What shape would you look for?

5. What are the properties of minerals?

2. Discussion point

Discuss the difference between a rock and mineral.

3. Put the proper word.

1. Solids that form naturally are ….

2. There are … kinds of minerals.

3. A solid Earth material, that usually is a mixture of several minerals is …

4. Retell the text.

30. MINERALS

Although many people use the word mineral, most do not know the geologic definition of a mineral or how a mineral is identified. For example, people often refer to the minerals needed in the diet. In the dietary sense, minerals are substances needed by the body that are not made from living things. These «minerals», such as iron, copper, sodium, calcium, iodide, magnesium, and zinc, are actually chemical elements that combine to from true minerals.

In contrast, in order for mineralogists to call something a mineral, it must meet four specific criteria. First, it must be inorganic; that is, it cannot be made from living things or their remains. Second, it must occur naturally in the Earth. Third, it must have a definite chemical makeup, whether it is made from a single element or from a compound. For example, sand is not a mineral because samples from different places usually contain different chemicals. Fourth, its atoms must be arranged in repeating patterns that form solids called crystals. Although there are a few exceptions, most minerals have all four of these qualities.