spinel group

Question 1

spinel formula

Answer 1

MgAl2O4

Question 2

spinel form

Answer 2

• isometric, octahedral or twinned
• dodecahedron as trucations
• other forms rare
• massive and irregular grains

Question 3

spinel hardness

Answer 3

8

Question 4

spinel specific gravity

Answer 4

3.5 to 4.1

Question 5

spinel color

Answer 5

• nonmetallic vitreous
• translucent to transparent clear
• shades of white, red, lavender, green blue brown black

Question 6

spinel occurrence

Answer 6

• high temp mineral in contact metamorphosed limestones and meta rocks poor in silica
• access mineral in many dark igneous rocks
• also rolled pebble in streams

Question 7

spinel remarks

Answer 7

• hardness, octahedral form, vitreous luster

Question 8

how to distinguish iron rich spinel from magnetite

Answer 8

spinel is non magnetic and has a white streak

Question 9

magnetite formula

Answer 9

Fe3O4

Question 10

magnetite form

Answer 10

• isometric, frequently in octahedral crystals, rarely in dodecahedrons
• other forms rare
• granular to massive coarse or fine grained

Question 11

magnetite cleavage

Answer 11

none, octahedral

Question 12

magnetite hardness

Answer 12

6

Question 13

magnetite specific gravity

Answer 13

5.18

Question 14

magnetite color

Answer 14

iron black, metallic opaque. black streak

Question 15

magnetite magnetism

Answer 15

natural magnet

Question 16

what do you call when magnetite acts as a natural magnet

Answer 16

lodestone

Question 17

magnetite occurrence

Answer 17

• commonly disseminated as access in most ign rocks
• in some ign rocks maybe main constituent and form large ore zones (TITANIFEROUS)
• also in metamorphic assemblages
• major constituent in precambrian banded iron formations
• in assoc with hematite and chert
• also in black sands along sea shores
• closely intergrown with corundum often

Question 18

what forms when magnetite and corundum are closely intergrown

Answer 18

emery

Question 19

magnetite remarks

Answer 19

strong magnetism, black color and 6 hardness

Question 20

chromite formula

Answer 20

FeCr2O4

Question 21

chromite form

Answer 21

• isometric, octahedral habit, rare in crystals
• commonly massive granular to compact

Question 22

chromite hardness

Answer 22

5.5

Question 23

chromite specific gravity

Answer 23

4.6

Question 24

chromite color

Answer 24

iron black to brownish black. dark brown streak
metallic to submetallic, pitchy
subtranslucent

Question 25

chromite occurrence

Answer 25

• common constituent of peridotites, other ultrabasic and serpentine
• assoc with olivine, serpentine and corundum

Question 26

chromite remarks

Answer 26

assoc with olivine and serpentine