Definition of a mineral: Naturally occurring Inorganic solid Ordered internal molecular structure Definite chemical composition

1. Minerals
By : Kornelis Eko Patty

2. Chapter 2 Opening Figure

3. Figure 2.1

4. Minerals: Building blocks of rocks
• Definition of a mineral:
• Naturally occurring
• Inorganic solid
• Ordered internal molecular structure
• Definite chemical composition
• Definition of a rock:
• A solid aggregate or mass of minerals

5. Physical properties of minerals
• Crystal Form
• External expression of the orderly
internal arrangement of atoms
• Crystal growth is often interrupted
because of competition for space and
rapid loss of heat

6. Figure 2.2

7. The mineral quartz often
exhibits good crystal form
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8. LUSTER – Does this look like it could
be made from a hard metal?
• Describes how light reflects off the surface
• Categories: Metallic or Non-metallic
Metallic – luster of metal – shines like a hard metal
(light does not penetrate)
Many non-metallic minerals are SHINY because they
are transparent or semi-transparent
• Non-metallic: vitreous or glassy; silky; pearly; greasy; waxy,
dull; earthy

9. Pyrite (fool’s gold) displays
metallic luster
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10. Examples of metallic luster

11. More Examples of Metallic Luster
PYRITE
Pyrite (FeS2)
Galena (PbS)
GALENA

12. Example of non-metallic luster
• Vitreous--quartz

13. Example of non-metallic luster
• Silky--example plagioclase feldspar

14. Non-metallic and metallic luster –
earthy hematite – metallic hematite

15. Physical properties of minerals
• Color
• Generally an unreliable diagnostic
property to use for mineral identification
• Often highly variable for a given mineral
due to slight changes in mineral
chemistry
• Exotic colorations of some minerals
produce gemstones

16. Quartz (SiO2) exhibits
a variety of colors
Citrine
Smoky
Quartz
Amethyst

17. Some Colors of Quartz

18. Physical properties of minerals
• Streak
• Color of a mineral in its powdered form
• Helpful in distinguishing different forms
of the same mineral
• Hardness
• Resistance of a mineral to abrasion or
scratching
• All minerals are compared to a standard
scale called the Mohs scale of hardness

19. Streak – the color of
a powdered mineral

20. STREAK
• 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.

21. Varieties of Hematite – all same color streak

22. Mohs scale of
hardness
HARDNESS –
Mineral’s
resistance to
scratching or
abrasion.
Minerals with
higher numbers
will scratch
minerals beside

23. Physical properties of minerals
• Cleavage
• Tendency to break along planes of weak
bonding
• Produces flat, shiny surfaces
• Described by resulting geometric
shapes
– Number of planes
– Angles between adjacent planes

24. Common
cleavage
directions
Figure 2.13

25. Three examples of perfect cleavage –
fluorite, halite, and calcite
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26. Cleavage – due to weak bonds in
the crystal structure
Halite (NaCl)
Fluorite (CaF2)
HALITE
FLUORITE

28. Cleavage
MUSCOVITE
BIOTITE

29. Physical properties of minerals
• Fracture
• Absence of cleavage when a mineral is
broken
• Specific Gravity
• Ratio of the weight of a mineral to the
weight of an equal volume of water
• Average value is approximately 2.7

30. Conchoidal fracture

31. Rose Quartz – Conchoidal Fracture

32. Conchoidal Fracture - Quartz
Obsidian

34. Density (Specific Gravity)
• All minerals have
density (mass /
volume), but some are
very dense
• Examples include
galena, magnetite,
and gold
• Specific Gravity is the
density of the mineral
compared with density
of water
http://www.minerals.net/mineral/elements/gold/gold1.htm

35. Physical properties of minerals
• Other properties
• Magnetism
• Reaction to hydrochloric acid
• Malleability
• Double refraction
• Taste
• Smell
• Elasticity
• Striations

36. Other Properties
• Magnetism - Property of a substance such
that it will spontaneous orient itself within a
magnetic field. Magnetite (Fe3O4) has this
property and it can be used to distinguish it
from other non-magnetite iron oxides, such
as hematite (Fe2O3).
• Straitions - Commonly found on plagioclase
feldspar. Straight, parallel lines on one or
more of the cleavage planes caused by
mineral twinning.
• Double Refraction - Seen in calcite crystals.
Light is split or refracted into two
components giving rise to two distinct
images.

37. Special Characteristics--
Magnetism
• Many iron minerals
will produce an
invisible magnetic
force field
• “Lodestone” was used
by Vikings more than
1,000 years ago as
compasses
http://www.minerals.net/mineral/oxides/magnetit/magneti4.htm

38. Acid Test for Carbonates
• Special Characteristics:
Carbonates react with dilute HCl and other
acids by fizzing or bubbling (releasing
CO2 gas)

39. Special Characteristics--
Fluorescence
• Some minerals will
glow when placed
under short-wave or
long-wave ultraviolet
rays
• Franklin and
Ogdensburg NJ are
famous for their
fluorescent minerals
http://www.sterlinghill.org/Tour%20information.htm

41. Special Characteristics--
Salty Taste
• DO NOT TASTE
MOST MINERALS!
• Halite is the
exception--it will taste
salty
http://mineral.galleries.com/scripts/item.exe?LIST+Minerals+Halides+Halite

43. Classification of Minerals
• Over 4000 minerals identified.
• Classification based on the key ion or
element that makes up the “building
block” of the mineral.
• An ion is an atom or molecule with an
unbalanced electrical charge.
• Most important group is the Silicate
Minerals, which form the majority of the
rock-forming minerals.

44. Classification of Minerals
Rock-forming minerals
• Common minerals that make up most of
the rocks of Earth’s crust
• Only a few dozen members
• Composed mainly of the 8 elements that
make up over 98% of the continental
crust

45. Elemental abundances
in continental crust
Figure 2.15

46. Classification of Minerals
• Silicates
• Most important mineral group
– Comprise most of the rock-forming minerals
– Very abundant due to large amounts of
silicon and oxygen in Earth’s crust
• Basic building block is the silicate ion
(aka the silicon-oxygen tetrahedron)
– Four oxygen ions surrounding a much
smaller silicon ion

47. Two
illustrations
of the
Silicate ion
Figure 2.16

48. Classification of Minerals
• Silicate structures
• Single silicate ions are linked together
to form various structures including
– Isolated ions
– Ring structures
– Single and double chain structures
– Sheet or layered structures
– Complex 3-dimensional structures

49. Classification of Minerals
• Common Silicate minerals
• Olivine
– High temperature Fe-Mg silicate
– Individual silicate linked together by iron
and magnesium ions
– Forms small, rounded crystals with no
cleavage

50. Figure 2.19a

51. Classification of Minerals
• Common Silicate minerals
• Pyroxene Group
– Single chain structures involving iron and
magnesium
– Two distinctive cleavages at nearly 90
degrees
– Augite is the most common mineral in the
pyroxene group

52. Figure 2.19b

53. Classification of Minerals
• Common Silicate minerals
• Amphibole Group
– Double chain structures involving a variety
of ions linking the silicate ion
– Two perfect cleavages at non right angles
Hornblende is the most common mineral in
the amphibole group

54. Figure 2.19c

55. Classification of Minerals
• Common Silicate minerals
• Mica Group
– Sheet structures that result in one direction
of perfect cleavage
– Biotite is the common dark colored mica
mineral
– Muscovite is the common light colored mica
mineral

56. Figure 2.19d

57. Figure 2.19e

58. Classification of Minerals
• Common Silicate minerals
• Feldspar Group
– Most common mineral group
– 3-dimensional framework that exhibits two
directions of cleavage at 90 degrees
– Orthoclase (potassium feldspar) and
Plagioclase (sodium and calcium feldspar)
are the two most common members

59. Figure 2.19f

60. Potassium feldspar
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Figure 2.19 F

61. Plagioclase feldspar
Figure 2.20

62. Classification of Minerals
• Common Silicate minerals
• Quartz
– Consists entirely of silicon and oxygen
(SiO2). This is a material called silica.
– Strong bonds in all directions – cleavage
absent.
– Naturally clear, but impurities cause colors.

63. Figure 2.19g

64. Classification of Minerals
• Important nonsilicate minerals
• Several major groups exist including
– Oxides
– Sulfides
– Sulfates
– Native Elements
– Carbonates
– Halides
– Phosphates

65. Classification of Minerals
• Important nonsilicate minerals
• Carbonates
Primary constituents in limestone; an
abundant marine sedimentary rock.
Calcite (calcium carbonate) and Dolomite
(calcium-magnesium carbonate) are the two
most important carbonate minerals.