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 its 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….)

3.2.2.1 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

3.2.2.2 Match the terms with their corresponding definition.

1. hardness	a. its weight relative to the weight of an unequal volume of water
2. habit	b. how a mineral reflects light
3. mineral	c. how a mineral parts along weaknesses in its crystal lattice
4. polymorph	d. random breakage of a mineral along no particular orientation
5. specific gravity	e. a consistent crystal shape, which is controlled by the chemical composition of a mineral
6.conchoidal fracture	f. its color in the powered form
7. luster	g. naturally occurring inorganic substances with a definite chemical composition and specific crystal structure
8. fracture	h. several physical forms of a mineral
9. cleavage	i. how a mineral resists scratching
10. streak	j. minerals break along characteristic curved surfaces that look like slightly concave, circular seashells