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into different shapes. Minerals, including gypsum and talc, that can be cut into thin
shavings are described as sectile. Still others, notably the micas, are elastic and will
bend and snap back to their original shape after the stress is released.
HARDNESS. One of the most useful diagnostic properties is hardness, a
measure of the resistance of a mineral to abrasion or scratching. This property is
determined by rubbing a mineral of unknown hardness against one of known hardness,
or vice versa. A numerical value of hardness can be obtained by using the Mohs scale of
hardness, which consists of 10 minerals arranged in order from 1 (softest) to 10
(hardest). It should be noted that the Mohs scale is a relative ranking, and it does not
imply that mineral number 2, gypsum, is twice as hard as mineral 1, talc. In fact,
gypsum is only slightly harder than talc, as FIGURE 12.1 B indicates.
CLEAVAGE. In the crystal structure of many minerals, some atomic bonds are
weaker than others. It is along these weak bonds that minerals tend to break when they
are stressed. Cleavage is the tendency of a mineral to break (cleave) along planes of
weak bonding. Not all minerals have cleavage, but those that do can be identified by the
relatively smooth, flat surfaces that are produced when the mineral is broken. Do not
confuse cleavage with crystal shape. When a mineral exhibits cleavage, it will break
into pieces that all have the same geometry.
FRACTURE. Minerals having chemical bonds that are equally, or nearly
equally, strong in all directions exhibit a property called fracture. When minerals
fracture, most produce uneven surfaces and are described as exhibiting irregular
fracture.

Task 4. Answer the following questions, using the vocabulary from Task 1.
1. What is determined by the type and strength of the chemical bonds?
2. What does the term tenacity describe?
3. When do we call minerals brittle? Malleable? Sectile? Elastic?
4. What diagnostic property is considered to be one of the most useful?
5. What is hardness?
6. How can a numerical value of hardness be obtained?
7. What is cleavage?
8. Do all minerals have cleavage?
9. What is the difference between cleavage and crystal shape?
10. What property do minerals having chemical bonds that are equally, or nearly
equally, strong in all directions exhibit?

Task 5. Complete the following sentences from the text in Task 3.
1. The term … describes a mineral’s toughness.
2. The term … describes a measure of the resistance of a mineral to abrasion or
scratching.
3. … is the tendency of a mineral to break (cleave) along planes of weak bonding.
4. When minerals fracture, most produce uneven surfaces and are described as
exhibiting … .
5. Minerals that are … tend to be brittle and shatter into small pieces when struck.
6. Minerals with … are malleable, or easily hammered into different shapes.

Task 6. Find English equivalents for the following (see the text).
Щоб описати міцність мінералів; як ламаються мінерали; твердість мінералів;
розколотись на маленькі шматочки; навпаки; легко розбити молотком на шматки
різної форми; порізати на тонку стружку; мінерали, що розташовані по порядку –
від найм’якіших до найтвердіших; зв’язки між атомами; ламатися під дією

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