2. Minerals
Minerals - naturaly formed, generally inorganic, crystalline,
solid and has a definite chemical composition.
building blocks of rocks
Mineralogy - Branch of Geology that deals with the study of
Minerals
There are about 3,000 known minerals, of that 20 minerals
make up most rocks
3. Physical Properties of Minerals
- can be used to easily identify a mineral.
1. Color
2. Streak
3. Hardness
4. Cleavage and Fracture
5. Crystalline structure
6. Transparency or diaphaneity
7. Magnetism
8. Tenacity
9. Luster
10. Odor
11. Specific Gravity
4. Physical Properties of Minerals
1. Color - usually the property used to identify minerals
easily. It is the result of the way minerals absorb light.
Some Colors of Quartz
6. Color
• Determined by the
chemical
composition of the
mineral
• Minerals rich in Al,
Ca, Na, Mg, Ba and
K are often light
coloured
• Minerals rich in Fe,
Ti, Ni, Cr, Co, Cu
and Mn are often
dark in colour
Haematite, Kidney Ore
8cm
7. Color 3
• Colour is not particularly useful
as a diagnostic property
• Some minerals show a wide variety of colours
• Quartz can be transparent, white, pink,
brown, purple, yellow, orange and even black
• Many minerals show very similar colours
• Calcite, gypsum, barytes, fluorite,
plagioclase feldspar and halite are
commonly grey or white in colour
10. Physical Properties of Minerals
2. Streak - is the color of the mineral in powder form.
For opaque minerals, if you rub the sample across a
streak plate, it will leave a colored powder. This
streak is distinctive for minerals and is used to identify
minerals.
13. Streak 2
Malachite – pale green Haematite – cherry red Iron Pyrite – greenish black
Galena – lead grey Sphalerite – pale brown Limonite – yellowish brown
15. Physical Properties of Minerals
3. Hardness - refers to the
measure of the mineral’s
resistance to scratching.
Minerals with higher
numbers will scratch
minerals below. To measure
the relative hardness of
minerals, the Moh's scale is
used.
16. Hardness
Measured on Moh’s scale from 1.0 (softest) to 10 (hardest)
Scale was devised by measuring the amount of noise and
powder produced from rubbing a mineral on a metal file
Talc 1.0 Diamond 10.0
19. Moh’s Scale of Hardness
Everyday objects can be substituted for minerals on Moh’s scale
Steel nail 5.5-6.0
Fingernail 2.5
Copper coin 3.0
Window glass 5.0
20. Testing For Hardness
Try to scratch mineral
specimens with substances
of known hardness
If a mineral is not scratched
by your fingernail, but is
scratched by a copper coin
then it will have a hardness
of 2.5–3.0
If a mineral cannot be
scratched by steel it has a
hardness of over 6.0
Gypsum is scratched by a
fingernail, hardness <2.5
21. Physical Properties of Minerals
4. Cleavage and Fractures - used to describe how minerals
break into pieces.
Some minerals split along flat surfaces (called
cleavage planes) when struck hard--this is called mineral
cleavage
Other minerals break unevenly along rough or curved
surfaces--this is called fracture
A few minerals have both cleavage and fracture
( mica )
23. Cleavage
The way a mineral breaks
when struck by a hammer
Cleavage is controlled by lines
of weakness in the atomic
structure of the mineral
Minerals can have 1, 2, 3
or 4 planes of cleavage
1 plane, parallel or
basal cleavage
2 planes of cleavage that
intersect at a characteristic angle
3 planes (cubic, rhombohedral)
4 planes, octahedral cleavage
24. Parallel or Basal Cleavage
One plane of cleavage enables the mineral to part along
parallel lines. It is analogous to a ream of paper that can
be separated into individual sheets.
Biotite Mica Barytes
1cm
1cm
25. Minerals Showing 2 Sets of Cleavage Planes
Feldspars – intersect at 90 degrees
Augite (Pyroxene) – intersect at 90 degrees
Hornblende (Amphibole) – Intersect at 60/120 degrees
Augite Plagioclase Feldspar
1cm
1cm
26. Prismatic Cleavage
Produced by the
intersection of three
cleavage planes
Cubic cleavage 3 planes
intersect at 90 degrees
e.g. halite
Rhombohedral cleavage
3 planes intersect at
60/120 degrees
e.g. calcite
Calcite
Halite
1cm
1cm
27. Octahedral Cleavage
Fluorite shows well
developed octahedral
cleavage
The cubic crystals are
truncated across their
corners at 45° by four
cleavage planes
This can eventually lead
to the formation of
octahedrons from the
original cubic crystals
Cleaved edge of
cubic crystal
1cm
Octahedron
Cleavage
Surface
32. Physical Properties of Minerals
5. Crystalline structure - crystal lattice, tells how a
mineral’s crystals are arranged. A hand lens is a
necessary tool in checking for crystalline structure.
crystal solid - form regular repeating three
dimensional crystal lattice
amorphous solid - forms aggregates that have
particular order or arrangement
33. Physical Properties of Minerals
6. Transparency or diaphaneity - indicates the extent of
light that can pass through the mineral.
34. 7. Magnetism
The ability of a mineral to attract iron filings and pick up steel pins
Magnets stick to magnetite quite readily and is the only
strongly magnetic mineral found at the earth’s surface
Octahedral crystals of Magnetite
Steel pins and magnet
attracted to magnetite
1cm
35. Physical Properties of Minerals
8. Tenacity - level of resistance or reaction of minerals to
stress such as crushing, bending, breaking, or tearing.
9. Luster - refers to the reaction of a mineral to light. It
determines how brilliant or dull the mineral is.
Categories: Metallic or Non-metallic
Metallic – luster of metal – shines like a hard metal
Many non-metallic minerals are SHINY because they
are transparent or semi-transparent
36. Lustre
The way in which a
mineral reflects light
Controlled by the atomic
structure of the mineral
Main types of lustre are
Vitreous
Metallic
Pearly
Resinous
Adamantine
Dull/Earthy
Quartz – Vitreous Lustre
2cm
39. Pearly Lustre
Biotite Mica
Muscovite Mica
The lustre of a pearl
or mother of pearl
Shows clearly on the
cleavage surfaces
of biotite and
muscovite mica
Also shown by Talc
and selenite (a variety
of gypsum)
40. Silky Lustre
The lustre of silk
Occurs in minerals with
a fibrous structure
Satin spar (a fibrous
form of gypsum) shows
this to good effect
1cm
Gypsum (Satin Spar)
41. Resinous Lustre
The lustre of resin
The mineral has a
grainy appearance
Sphalerite, opal
and amber show
resinous lustre
Sphalerite (Zinc Blende)
1cm
43. Dull or Earthy Lustre
The mineral does not
reflect light and has the
same appearance as soil.
Minerals such as galena
have metallic lustres on
freshly broken surfaces
but they tarnish to dull
with prolonged exposure
to the atmosphere
1cm
Limonite has a dull or earthy lustre
44. Physical Properties of Minerals
10. Odor - -a distinct smell of a mineral that is usually
released from a chemical reaction when subjected to water,
heat, air or friction.
11. Specific Gravity - is a measure of the density of a
mineral. Determines how heavy the mineral is by its weight
to water.
45. 12. Transparency
Calcite – Iceland Spar
• When outlines of objects
seen through it appear
sharp and distinct
• A good examples is Iceland
Spar, a variety of calcite that
is used for optical lenses
•Iceland Spar also shows the
remarkable property of
double refraction
• Determined by the atomic
structure and chemical
composition of the mineral
2cm
46. 13. Translucency
Fluorite
1 cm
•The ability for a mineral to
let light pass through it
•Many minerals if cut thin
enough will show some
degree of translucency
•Controlled by atomic
structure and chemical
composition
•All transparent minerals
are also translucent
47. 14. Taste
If a mineral can be
tasted in the mouth,
then it is soluble in
fresh water
Halite (rock salt)
tastes salty and is a
diagnostic property
of the mineral
48. 15. Striking Fire With Steel
Iron Pyrite (Fools
Gold) sparks when
struck with a steel
hammer and releases a
sulphurous odour
Iron Pyrite was used
as flints in flintlock
pistols to ignite the
gunpowder
Pyritohedrons
Pyrite cubes
49. 16. Feel
A characteristic sensation experienced when a
mineral is held and rubbed between the fingers
Graphite feels very cold
upon the touch as it is a
very good conductor of heat
2cm 2cm
Talc feels very greasy when
rubbed between the fingers
50. Chemical Properties of Minerals
Another way of identfying and classifying minerals is
according to their chemical compositon. This classification
was first used in 1848 by James Dwight Dana (1813-
1895).
1. Silicate class 5. Oxide class
2. Carbonate class 6. Sulphide class
3. Sulphate class 7. Phosphate class
4. Halide class 8. Native element class
51. Chemical Properties of Minerals
1. Silicate Class - largest and most abundant group
containing Si and O with some Al, Mg, Fe, and Ca.
(Ex. feldspar, quartz, pyroxene, mica, garnet. olivine
and amphibole
52. Chemical Properties of Minerals
2. Carbonate class - mostly found deposited in marine
environments.
3. Sulphate Class - forms in areas with high
evaporation rates and where salty waters slowly
evaporate.
(Ex. anhydrite, celestine, barite, gypsum)
4. Halide class - contains natural salts includes fluorite,
halite, sylvite and sal ammoniac components. Usually
form in lakes, and sal ammoniac components.
53. Chemical Properties of Minerals
• 5. Oxide class - is a diverse class. In science,
these minerals are important as thet carry histories
of changes in Earth's magnetic field. They are
formed as precipitates close to Earth's surface or
as oxidation products of minerals during the
process of weathering.
• 6. Sulphide class - has important metals such as
copper, lead and silver which are considered
economically significant.
54. Chemical Properties of Minerals
7. Phosphate class- contains minerals with
phosphorus. Considered as important biological
mineral found in teeth and bones in many
animals.
8. Native element class - contains metals and
intermettalic elements, semimetals nonmetals
or natural alloys and constituents of a few rare
meteorites.
