sulfides 13-16 SET 4

Question 1

marcasite formula

Answer 1

FeS2

Question 2

marcasite crystal form

Answer 2

• orthorhombic, polymorphous with pyrite
• commonly tabular, less commonly prismatic parallel
• often twinned, giving cockscomb and spear-headed groups
• usually in radiating forms
• often stalactitic, inner core with radiating structure and covered with irregular crystal groups
• also globular and reniform

Question 3

marcasite hardness

Answer 3

6 to 6.5

Question 4

marcasite specific gravity

Answer 4

4.89

Question 5

marcasite color

Answer 5

pale bronze yellow to almost white on fresh fracture
tarnish: yellow to brown
streak: gray black

Question 6

marcasite occurrence

Answer 6

• in metalliferous veins, with lead and zinc
• less stable than pyrite, easy to decompose, less common
• supergene mineral at low temp near surface
• replacement deposits in limestone and concretions in shales

Question 7

how to distinguish pyrite and marcasite

Answer 7

paler yellow color, also it has a fibrous habit??

Question 8

Molybdenite formula

Answer 8

MoS2

Question 9

Molybdenite crystal form

Answer 9

• hexagonal, in plates or short tapering prism
• commonly foliated, massive or in scales

Question 10

Molybdenite cleavage

Answer 10

perfect basal, flexible not elastic

Question 11

Molybdenite hardness

Answer 11

1 to 1.5 greasy

Question 12

Molybdenite specific gravity

Answer 12

4.62 to 4.73

Question 13

Molybdenite color

Answer 13

lead gray, with grayish black streak

Question 14

Molybdenite occurrence

Answer 14

• accessory mineral in some granites, in pegmatites and aplites
• common in high temp vein deposits with cassiterite, scheelite and fluorite
• in contact metamorphism with ca silicates, scheelite and chalcopyrite

Question 15

how to distinguish Molybdenite from graphite

Answer 15

moly has higher specific gravity and has a blue tone color, while graphite has brown tinge. graphite also has black streak while moly has greenish

Question 16

Arsenopyrite formula

Answer 16

FeAsS

Question 17

Arsenopyrite crystal form

Answer 17

• monoclinic, prismatic
• elongated on c, less common on b
• granular and compact

Question 18

Arsenopyrite cleavage

Answer 18

prismatic poor

Question 19

Arsenopyrite hardness

Answer 19

5.5 to 6

Question 20

Arsenopyrite specific gravity

Answer 20

6.07

Question 21

Arsenopyrite color

Answer 21

silver white, with black streak

Question 22

Arsenopyrite occurrence

Answer 22

• most common mineral with arsenic
• occurs with tin and tungsten ores in high temp hydrothermal deposits
• associated with silver and copper ores
• accessory mineral in pegmatites, and contact metamorphism
• disseminated in crystalline limestone

Question 23

how to distinguish Arsenopyrite from marcasite

Answer 23

Arsenopyrite is silver white, marcasite is pale yellow to almost white

Question 24

enargite formula

Answer 24

Cu3AsS4

Question 25

enargite crystal form

Answer 25

• orthorhombic, elongated parallel to c and vertically striated
• tabular parallel on 001
• bladded, columnar and massive

Question 26

enargite cleavage

Answer 26

prismatic perfect and distinct

Question 27

enargite hardness

Answer 27

3

Question 28

enargite specific gravity

Answer 28

4.45

Question 29

enargite color

Answer 29

black to iron black
grayish black to iron black streak

Question 30

enargite occurrence

Answer 30

• in veins replacement deposits at mod temps assoc with pyrite, sphalerite, bornite, galena and chalcocite

Question 31

enargite remarks

Answer 31

its color and cleavage, striated crystals as well