Fig. 18 Pyrite cube showing metallic luster (Photo by John Bett) Fig. 19 Vitreous luster on quartz crystal faces (Photo by John Bett)

metallic	submetallic	nonmetallic
Bright		Adamantine (bright)
Dull		Vitreous (glassy)
		Pearly
		Waxy
		Silky
		Greasy
		Resinous
		Earthy (dull)

Besides the above-mentioned description of luster there is no standard scale currently in use.

7. How a mineral parts along weaknesses in its crystal lattice is referred to as cleavage. Cleavage is often very diagnostic as a mineral identification method since weaknesses in the crystal lattice will always be consistent in the same mineral. Quartz is tightly bonded in their crystalline structure and produces no cleavage. Mica has one direction of cleavage while calcite has three directions.

Fig. 20 Biotite, demonstrating the perfect cleavage parallel to the crystal sheet

8. Random breakage of a mineral along no particular orientation is referred to as its fracture. Quartz and some other similar silicate minerals break along characteristic curved surfaces that look like slightly concave, circular

seashells. These are called conchoidal fractures and can also be found along chipped edges of window glass.

Fig. 21 Conchoidal fracture

9. Some minerals have very distinctive taste qualities that facilitate their
immediate identification. Rock salt (halite) and sylvite are two minerals with
distinctive tastes.

10. A few minerals respond to common chemical reagents. Calcite responds
to hydrochloric acid. Dolomite responds weakly to hot hydrochloric acid but
reacts more when it is powered.

11. Radioactive minerals emit particles that activate various types of
detectors and counters.
(Geology Link- http://college.hmco.com\geology\resources….)

State what are the synonyms to the following words. Pay attention to the meaning of the word in the text.

1. guideline
2. consistent
3. value
4. assist in
5. be obtained by
6. unglazed
7. lattice
8. be bonded in

9. random
10. orientation
11. chipped edges
12. distinctive
13. facilitate
14. counter

Match the terms with their corresponding definition.

1. hardness 2. habit 3. mineral 4. polymorph 5. specific gravity 6.conchoidal fracture 7. luster 8. fracture 9. cleavage 10. streak

a. its weight relative to the weight of an unequal
volume of water

b. how a mineral reflects light

c. how a mineral parts along weaknesses in its crystal
lattice

d. random breakage of a mineral along no particular
orientation

e. a consistent crystal shape, which is controlled by the
chemical composition of a mineral

f. its color in the powered form

g. naturally occurring inorganic substances with a
definite chemical composition and specific crystal
structure

h. several physical forms of a mineral

i. how a mineral resists scratching

j. minerals break along characteristic curved surfaces

that look like slightly concave, circular seashells

Give examples of the following physical properties of minerals FOR EXAMPLE: Quartz can be of nearly any color because of slight mineral impurities. Quartz can be cloudy, white, pink, purple, red, black, smoky, orange and brown.

1. color –                                      6. streak –

2. luster –                                     7. specific gravity –

3. hardness –                                8. taste –

4. cleavage –                                 9. chemical reagents –

5. fracture –                                  10. crystal system –

3.3 DETAILED READING – Basic rock types (R.P – 4.2) Read the following text and fulfill the following task- state which statements are T (TRUE) or F (FALSE):

Geologists recognize three main rock-forming processes, therefore, three principal classes of Earth-forming substances. In the first process, molten rock, or magma, solidifies either to glass or to an aggregate of one or more minerals, or to some combination of glass and minerals; such rocks are termed igneous. Ignis is the Latin word for “fire”; igneous rocks are, in a sense, formed from fire deep inside the Earth. Lava flows and ash falls are good examples. Sedimentary rocks consist of mechanically accumulated fragments of preexisting Earth materials, as well as, chemical or biochemical precipitations from a fluid medium. Sedimentum is the Latin for “a settling”, and sedimentary rocks have had their constituents settle out from the transporting medium, either air or, more generally, water. Such processes take place at the Earth’s surface. Metamorphic rocks include all those rocks whose original minerals or textures, or both have been altered markedly by recrystallization or deformation; metamorphism generally takes place at considerable depth within the Earth. The Greek word meta is translated as “successive” or “change”; a metamorphic rock represents a later configuration of minerals or textures different from those of the original material. (Barret E., Hunt A. And Milner B.” Earth and Atmosphere”, 1993, Longman)