5. some minerals

Question 1

Olivine

Answer 1

• Nesosilicates
• Forms only in igneous ultramafic rocks
• Typical in basaltic rocks
• The green colour shade is typical
• First mineral to crystallize in Bowen’s reaction series
• Lustre: vitreous
• Fracture: conchoidal

Hardness: 6,5 to 7

Question 2

Garnet

Answer 2

• Nesosilicates
• Forms almost exclusively in metamorphic rocks
• Mostly red (but not necessarily)
• Lustre: vitreous
• Fracture: conchoidal, brittle

Hardness: 6,5 to 7

Question 3

Epidote

Answer 3

• Sorosilicates
• Forms only in metamorphic rocks
• Typical by low pressure and temperature conditions
• The green colour shade is typical and different to olivine
• Lustre: vitreous
• conchoildal and irregular fracture

Question 4

Tourmaline

Answer 4

• Cyclosilicates
• Among others accessory mineral in pegmatite and metamorphically overprinted sedimentary rocks (metasedimentary rocks)
• Colour: mostly black
• Lustre: vitreous

Question 5

Augite (pyroxene)

Answer 5

• Single-chain inosilicates
• Forms almost exclusively in igneous rocks
• Among others typically in basalt
• Colour: Black, green and many more
• Cleavage planes: 87° & 93° to each other
• Lustre: vistreous to dull
• Streak: Bronw to greennish-gray

Question 6

Hornblende (amphibole)

Answer 6

• Double-chain inosilicates
• Forms both in igneous and in metamorphic rocks
• May occur among others both in granite and in basalt, as well as in gneiss
• Colour: Black, green and many more
• Cleavage planes: 56° & 124° to each other (distinguishing it from pyroxene)
• Cleavage along two planes not at 90 degrees

Question 7

Mica - Biotite

Answer 7

• Phyllosilicates
• Biotite (black) and muscovite (colourless) occur both in igneous (biotite more common) and metamorphic rocks (muscovite more common).
• Cleavage along one plane

Question 8

Mica - Muscovite

Answer 8

• Phyllosilicates
• Biotite (black) and muscovite (colourless) occur both in igneous (biotite more common) and metamorphic rocks (muscovite more common).
• Cleavage along one plane
• Elasticity: mica (glimmer; f. ex. biotitt & muskovitt) sheets can be bent & snap back elastically.
• Pearly luster

Question 9

Glauconite

Answer 9

-Phyllosilicates
- Glauconite forms in the ocean at low sedimentation rates. It makes the sediment green.
Lustre: dull to earthy
- Cleavage along one plane

Question 10

Illite and Kaolinite

Answer 10

• Phyllosilicates
• Crystals typical of clay size
• Common in sedimentary rocks - they form at low P & T
• Illite is dark, kaolinite is white.

Question 11

Chlorite

Answer 11

• Phyllosilicates
• Forms & occurs in many low-grade metamorphic rocks (NOT in igneous rocks)
• Colour: Dark green (darker than olivine & epidote)

Question 12

Alkalifeldspar

Answer 12

• Tectosilicates
  Cleavage along two planes at 90 degrees
• Feldspar is colourless, but may be coloured by impurities.
  K feldspar often is red.
• Alkalifeldspar is more common in felsic (light-coloured) igneous rocks
• Particularly alkalifeldspar forms also in metamorphic rocks

Question 13

Plagioclase

Answer 13

• Tectosilicates
• Feldspar is colourless, but may be coloured by impurities. K feldspar often is red.
• Plagioclase is more common in mafic (dark) igneous rocks
• Good cleavage

Question 14

Quartz

Answer 14

• Tectosilicates
• Colour: Colourless - impurities may cause other colours
• Commonly formed both in igneous & metamorphic rocks
• Main constituent of most sandstone
• Flint is a microcrystalline variety of quartz
• Conchoidal fracture
• Vitreous luster
• Moh’s scale = 7

Question 15

Magnetite

Answer 15

• Oxide
• The most magnetic mineral that exists
• Colour: black
• Occurs in all rock types - particularly in mafic (dark, Fe and Mg rich) igneous rocks
• conchoidal fracture
• magnetic

Question 16

Hematite

Answer 16

• Oxide
  Hematite = rust
• Native Fe & magnetite may oxidate to hematite
• Colour: rusty red - brown - black
• Forms as one (of several) weathering product from less stable minerals (e. g., olivine, pyroxene) - the red colour of tropical soil is caused by hematite

Question 17

Ilmenite

Answer 17

• oxide
• Weakly magnetic
• Colour: black to grey
• Particularly common as accessory mineral in mafic igneous rocks - it is often associated with magnetite
• Tellnes mine (Sokndal) is one of the largest open-cast ilmenite mines in the world
• metallic to submetallic luster
• conchoidal fracture

Question 18

Goethite

Answer 18

• Hydroxide
• Colour: yellow to brown
• Forms due to oxidation of Fe oxides (magnetite, hematite)
• Can form as precipitate from water, “bog ore”. Therefore it commonly is found in sedimentary rocks.

Question 19

Pyrite

Answer 19

• Sulphide
• The most common sulphide mineral
• Alters easily to Fe oxide
• Colour: golden yellow ( “fool’s gold”)
• The crystals usually form cubes.
• May form in most rock types. In sediments it forms in anaerobic environments. It may replace the organic material of fossils.

Question 20

Gypsum

Answer 20

• Sulphade
• The most common sulphate mineral
• Forms primarily as evaporite by precipitation
• Highly soluble in water
• Colour: colourless to white (due to gas bubble inclusions in the crystal lattice)
• Very soft
• May form “desert roses”
• Hardness 2

Question 21

Anhydrite

Answer 21

-Sulphade
- Forms secondarily from gypsum
(the water is released at increased T)
- Highly soluble by water
- Colour: colourless to white
- Very soft

• Perfect cleavage

Question 22

Aragonite

Answer 22

• Carbonate
• Very similar to calcite
• The same chemical composition as calcite but a different crystal structure
• calcite & aragonite are polymorphs
• Both mainly form from (different) organisms
• Both are colourless to white
• Both are soluble in acid
• Both may dissolve in water

Question 23

Calcite

Answer 23

• Carbonate
• Cleavage along three planes at not 90 degrees
• Double refraction: When calcite is placed over a printed paper, the letters will appear doubled
• Solubility (HCl test): Most Ca carbonates (e. g., calcite) dissolve in acid
• Moh’s scale = 3

Question 24

Dolomite

Answer 24

• Carbonate
• Secondary mineral
• Colourless to white
• Forms from alteration of calcite & aragonite + Mg in water (= dolomitisation).
• Dissolves in hot HCl
• May dissolve in water

Question 25

Apatite

Answer 25

• Phosphate
• Colour: green, colourless, yellow & many other colours
• Most important phosphate mineral - fertilizer
• Common accessory mineral in magmatic, metamorhic & sedimentary rocks
• The mineral that build up our teeth and our skeleton (and those of many other animals)
• Collophane: special name on tooth & skeleton remains in sediment (brown colour)
• Dissolves in acid

Question 26

Halite

Answer 26

• Halides
• Cleavage along three planes at 90 degrees
• Taste: halite tasts salty
• Evaporite mineral
• Colourless
• Form perfect crystal cubes
• Easily dissolves in water
• The main constituent of most salt diapirs (e. g., Permian Zechstein deposits in the North Sea & central Europe)

Question 27

Fluorite

Answer 27

• Halides
• Cleavage along four planes
• Moh’s scale = 4
• • Many colours
• Fluorescent mineral (produces light during ultraviolet radiation)
• Common in hydrothermal veins and as accessory mineral in igneous rocks