بنك الاسئلة EMR 2010 2ND SEMESTER 311

I. Choose the correct answer: (8 Marks)

1. The gem quality variety of olivine is called …………………

a) aquamarine.                                   b) emerald.

c) morganite .                                    d) peridot.

2. Staurolite shows ………………….. twinning.

a) simple                                            b) lamellar

c) elbow                                             d) interpenetration

3. Normally, zircon contains …………….. hafnium (Hf).

a) 30 %                                               b) 10-40 %

c) zero %                                            d) 1-4 %

4. ……………… is a green variety of microcline.

a) Emerald                                          b) Amazonite

c) Peridot                                            d) Monazite

5. Blue asbestos (crocidolite) is ………………….

a) an amphibole mineral.                    b) a pyroxene mineral.

c) a mica mineral.                               d) a serpentine mineral.

6. Wollastonite is ……………………..

a) an asbestos mineral.                       b) a pyroxene mineral.

c) a pyroxenoid mineral.                    d) an amphibole mineral.

7. Glaucophane is a ……………………

a) high-P amphibole.                          b) high-P pyroxene.

c) high-P silica.                                  d) high-P, high-T amphibole.

8. The pinkish variety of beryl is called ……………………..

a) aquamarine.                                    b) emerald.

c) morganite.                                      d) peridot.

II. Complete the following statements: (8 Marks)

1.     Perthite is an intergrowth of minute plagioclase in a K-feldspar host.

2.     Kaersutite is a Ti-rich amphibole found in some intermediate volcanic rocks.

3.     CaTiSiO₅ is the chemical formula of titanite.

4.     Sanidine is a K-feldspar that is found only in volcanic rocks, e.g. trachyte.

5.     Tourmaline with pinkish core and green rim is called watermelon tourmaline.

6.     Amosite is brown amphibole asbestos.

7.     High-pressure SiO2 polymorphs are stishovite and coesite.

V. Give reasons: (8 Marks)

1. Hemimorphite is a supergene mineral.

Hemimorphite is a secondary hydrated Zn-silicate mineral that forms as a result of primary Zn ore (mostly sphalerite, ZnS) oxidation. So, it is safe to say that hemimorphite is a supergene mineral since it is found as a gossan mineral capping unexposed Zn sulphide ores (hypogene).

2. Andalusite is common in hornfelses.

Andalusite is formed by metamorphism in low-pressure conditions, so it is expected to find the minerals in hornfelses formed by thermal metamorphism where high pressure is lacking.

3. Chrysotile asbestos is a dangerous mineral.

Chrysotile habit is often short fibers that can be inhaled by humans or animals and causes severe lung problems and it is simply carcinogen.

4. Feldspathoids are rare in granites.

Feldspathoids are tectosilicate minerals that have silica deficiency and hence they are not common in granitic rocks. Some peralkaline granites may bear few of them occasionally.

VI. State whether false or true, then correct the false ones: (4 Marks)

1. Cordierite is a low-P Al₂SiO₅ mineral.

(False)

Cordierite is a low-P mineral but its chemical formula is not Al₂SiO₅ but (Mg,Fe)₂Al₄Si₅O₁₈·nH₂O.

Or

Andalusite is a low-P Al₂SiO₅ mineral.

2. Zoisite is a sorosilicate mineral.

(True)

3. Sillimanite and chrysotile are fibrous minerals.

(True)

4. Density of fayalite is higher than that of forsterite.

(False)

Forsterite is heavier than fayalite.