5. some minerals Flashcards
1
Q
Olivine
A
- 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
2
Q
Garnet
A
- Nesosilicates
- Forms almost exclusively in metamorphic rocks
- Mostly red (but not necessarily)
- Lustre: vitreous
- Fracture: conchoidal, brittle
Hardness: 6,5 to 7
3
Q
Epidote
A
- 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
4
Q
Tourmaline
A
- Cyclosilicates
- Among others accessory mineral in pegmatite and metamorphically overprinted sedimentary rocks (metasedimentary rocks)
- Colour: mostly black
- Lustre: vitreous
5
Q
Augite (pyroxene)
A
- 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
6
Q
Hornblende (amphibole)
A
- 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
7
Q
Mica - Biotite
A
- Phyllosilicates
- Biotite (black) and muscovite (colourless) occur both in igneous (biotite more common) and metamorphic rocks (muscovite more common).
- Cleavage along one plane
8
Q
Mica - Muscovite
A
- 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
9
Q
Glauconite
A
-Phyllosilicates
- Glauconite forms in the ocean at low sedimentation rates. It makes the sediment green.
Lustre: dull to earthy
- Cleavage along one plane
10
Q
Illite and Kaolinite
A
- Phyllosilicates
- Crystals typical of clay size
- Common in sedimentary rocks - they form at low P & T
- Illite is dark, kaolinite is white.
11
Q
Chlorite
A
- Phyllosilicates
- Forms & occurs in many low-grade metamorphic rocks (NOT in igneous rocks)
- Colour: Dark green (darker than olivine & epidote)
12
Q
Alkalifeldspar
A
- 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
13
Q
Plagioclase
A
- 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
14
Q
Quartz
A
- 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
15
Q
Magnetite
A
- 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
16
Q
Hematite
A
- 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
17
Q
Ilmenite
A
- 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
18
Q
Goethite
A
- 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.
19
Q
Pyrite
A
- 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.
20
Q
Gypsum
A
- 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
21
Q
Anhydrite
A
-Sulphade
- Forms secondarily from gypsum
(the water is released at increased T)
- Highly soluble by water
- Colour: colourless to white
- Very soft
- Perfect cleavage
22
Q
Aragonite
A
- 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
23
Q
Calcite
A
- 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
24
Q
Dolomite
A
- Carbonate
- Secondary mineral
- Colourless to white
- Forms from alteration of calcite & aragonite + Mg in water (= dolomitisation).
- Dissolves in hot HCl
- May dissolve in water
25
Q
Apatite
A
- 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
26
Q
Halite
A
- 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)
27
Q
Fluorite
A
- 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
