Minerals

Question 1

Definition of Minerals

Answer 1

Any naturally occurring, inorganic substance with with a definite chemical composition and a definite atomic structure. (i.e crystalline). e.g Silicon Dioxide (Silica), Quartz- symmterical structure, Glass- amorphous (random).

Question 2

What are rocks?

Answer 2

Solid portion of the Earth that has a recognisable appearance and composition. A rock is a collection of minerals.

Question 3

Granite composition

Answer 3

Quartz, mica, feldspar.

• Sodium plagioclase feldspar (Na feldspar)
• Potassium feldspar (K feldspar
• Quartz
• Accessory biotite, amphibole, or muscovite

Question 4

Common elements in the Earth’s Crust

Answer 4

Element               Abundance by weight (%)
Oxygen (O)          45.2
Silicon (Si)            27.2
Aluminium (Al)     8.0
Iron (Fe)               5.8
Calcium (Ca)        5.06
Magnesium (Mg) 2.77
Natrium/Sodium 
(Na)                      2.32
Potassium (K)      1.68
Titanium (Ti)        0.86
Hydrogen (H)      0.14
Manganese (Mn) 0.1 
Phosphorus (P)    0.1

Question 5

Rock-Forming Minerals

Answer 5

Silicates

• Quartz SiO2
• Orthoclase feldspar (potassium feldspar) K Al Si O
• Plagioclase feldspar (calcic-sodic feldspar) Ca Na Al Si O
• Muscovite Mica H K Al Si O
• Biotite Mica H K Fe Mg Al Si O
• Hornblende H K Na Ca Mg Fe Al Si O
• Augite Ca Mg Fe Al Si O
• Olivine Fe Mg Si O

Carbonates
-Calcite CaCO3

Question 6

What are the Physical Properties of Identifying Minerals?

Answer 6

• Colour, Streak and lustre
• Hardness
• Cleavage and fracture
• Specific Gravity
• Magnetism
• Acid Reaction

Question 7

Colour, streak and lustre

Answer 7

Colour

• result of minerals light-absorbing/light-reflecting properties
• Varies in vitreous minerals due to the presence of trace impurities
• More reliable in opaque minerals

Streak
-Colour of its powder when rubbed along an unglazed porcelain
plate (streak plate)- maybe be different from colour of mineral itself.
-Scratching the mineral with a knife may also produce powder.
-Streak is consistent for that mineral despite any differences in colour

Lustre
-Appearance due to the amount and quality of light reflected from surface
-Seven main types of lustre:
1 Adamantine- the lustre of diamond
2 Vitreous- the lustre of broken glass e.g Quartz
3 Resinous- the lustre of resin, e.g amber and opal
4 Waxy- the lustre of thin layer of oil
5 Pearly- the lustre of pearl
6 Silky- the lustre of silk in fibrous minerals such as satin spar gypsum
7 Metallic- the lustre of metal (submetallic- as metallic, poorly displayed)

Question 8

Mohs Scale of Hardness

Answer 8

Talc 1
Gypsum 2
Calcite 3
Fluorite 4
Apatite 5
Orthoclase 6
Quartz 7
Topaz 8
Corundum 9
Diamond 10

Question 9

Describe Cleavage

Answer 9

-Tendency of mineral to break along flat, planar surfaces as determined
by its crystal lattice/structure
-Known as cleavage planes and caused by alignment of weaker bonds
between atoms in the crystal lattice
-Cleavage planes are distinguished from fracture by being smooth and often
having reflective surfaces

Question 10

Cleavage Terms

only use if cleavage planes can be recognised

Answer 10

• Perfect- smooth surfaces (often seen as parallel sets of straight lines), e.g mica
• Imperfect- planes that are not smooth e.g pyroxene
• Poor-Less regular
• Non-existent

Question 11

Fracture (+terms)

Answer 11

The way a mineral breaks other than along a cleavage plane.
Fracture terms:
*Conchoidal- Fracture surface is a smooth curve, bowl-shaped (common in glass)
*Imperfect- planes that are not smooth, e.g. pyroxene
*Hackly- Fracture surface has sharp, jagged edges
*Uneven- Fracture surface is rough and irregular
*Fibrous- Fracture surface shows fibres or splinters

Question 12

Specific Gravity

Answer 12

-How much greater the weight of the mineral is to an equal amount
of water
-Water has a specific gravity of 1.0
-If a mineral has a specific gravity of 2.7, it is 2.7 times heavier than water
SpGr= sample density/water density

Question 13

Magnetism

Answer 13

Several minerals react when placed within a magnetic field. Some minerals are:

• Strongly attracted to the magnet (ferromagnetism e.g. magnetite)
• Weakly Attracted (paramagnetic - e.g. hematite)
• One mineral is repelled (diamagnetism- bismuth)

Question 14

Acid Reaction

Answer 14

A drop of 5-10% hydrochloric acid (HCl) is placed on a mineral to see if CO2 bubbles
are released (might require hand lens).
Minerals and rocks with CO3 in them will release CO2 when in contact with HCl.

Florescence- some minerals fluoresce under UV light (calcite, rhyolite).