Download Mineral: is a homogeneous substance that Mineral: is a

MINERALS
Building blocks of rocks
Mineral: is a homogeneous substance that
has a
definite chemical composition and
an orderly geometric arrangement
of atoms.
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Minerals:
•
Naturally occurring
•
Inorganic solid
•
Ordered internal molecular structure
•
Definite chemical composition
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1
Nearly 4000 minerals have been
identified on Earth.
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Identification of Minerals
Minerals can be only identified absolutely by X‐ray analysis and chemical tests.
The x‐ray analysis determines the structure of the mineral and the chemical tests determine the composition of the mineral. Structure and composition are the defining marks of a mineral. 4
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X‐ray analysis
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Unfortunately, these tests require:
• expensive equipment, expert know‐how and
• expert know‐how and • often destroy the specimen. Fortunately, both structure and composition affect certain physical properties. It is through the proper use of these properties that minerals can reliably be identified. 6
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The Physical Properties of Minerals
• Structure (Crystal Form)
• Hardness
• Cleavage
• Fracture
• Specific Gravity
• Color
• Streak
• Luster
• Tenacity
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Crystal Form
• is the external shape produced by a minerals internal crystalline structure.
internal crystalline structure.
• This happens when a mineral grows (or solidifies) without interference or obstacle.
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4
ISOMETRIC
DIAMOND
TETRAGONAL
WULFENITE
HEXAGONAL
BERYL
TRIGONAL
QUARTZ
variety AMETHYST
ORTHORHOMBIC
TANZANITE
MONOCLINIC
GYPSUM
TRICLINIC
MONTEBRASITE
AMORPHOUS
AMBER
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Hardness
• is a measure of a mineral's resistance to abrasion.
• is determined by the relative ease or difficulty with which one mineral can scratch another. • U
Using known mineral samples
i k
i
l
l to test the hardness of h h d
f
an unknown is common practice.
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Hardness
• With a systematic approach, you can use minerals of known hardness
i
l fk
h d
t d t
to determine the i th
relative hardness of any other mineral.
• A mineral of a given hardness will scratch a mineral of a lower number. mineral of a lower
number
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You can use the following items to help estimate the hardness of a mineral:
•
Finger Nail (H = 2.5)
•
Penny (H = 3)
•
Knife Blade (H = 5.5)
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The Mohs Hardness Scale:
Hardness number
1 2
2 3 Mineral
Talc
Gypsum
Calcite
4 5 6 7 8 9 Fluorite
Apatite
Orthoclase
Quartz
Topaz
Corundum
10 Diamond
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#1 Talc
#5 Apatite
#8 Topaz
#2 Gypsum
#6 Orthoclase
#9 Corundum
MINERAL
Hardness scale:
1 Talc
2 Gypsum
3 Calcite
4 Fluorite
5 Apatite
6 Orthoclase
7 Quartz
8 Topaz
9 Corundum
10 Diamond
#3 Calcite
#7 Quartz
#10 Diamond
#4 Fluorite
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7
Fracture and Cleavage
• If a mineral fractures, it breaks along rough ,
g
g
edges. • If it cleaves, then it breaks along smooth, g
flat surfaces. 15
Cleavage
is the tendency of a mineral to break in certain
preferred directions
along smooth planes.
planes.
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8
Cleavage
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Fracture
• is a description of the way a mineral tends to b k
break. • It is different from cleavage .
• The broken surface is irregular.
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FRACTURE
The most common fracture type is:
• Smooth or rough curved break Conchoidal
• Fibrous or splintery break
Splintery
• Rough surface with sharp edges Hackley
• Rough surface Uneven
Rough surface
Uneven
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Conchoidal Fracture (Quartz and Obsidian)
When some minerals fracture, they appear to break • along long curved surfaces (that looks like a shell) • This type of fracture is known as conchoidal
Thi t
ff t
i k
h id l fracture f t
• Quartz and the igneous rock Obsidian will demonstrate this type of fracture. 20
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Splintery
Minerals such as asbestos break into long fibrous.
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Specific Gravity
• Specific gravity is a measure of the density of a mineral. • IIt is derived from the density of the mineral divided by the density of i d i df
h d i
f h
i
l di id d b h d i
f
water. • At times it is such a useful property that it is the only way to distinguish some minerals without laboratory or optical techniques. Example: • Gold can easily be distinguished from “fool's gold, Pyrite"
by specific gravity alone, although there are many other ways. 22
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Specific Gravity
Minerals
Specific gravity
• sulfur, graphite 1‐2
• gypsum, quartz, calcite 2‐3
• fluorite, beryl
3‐4
• corundum, most metal oxides, pyrite 4‐6
• native gold, platinum 19
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COLOUR
• Color is the first thing someone notices when they view a mineral Color is also one of the big reasons
view a mineral. Color is also one of the big reasons that attract people to minerals. • Generally speaking, color is not a good property to be used in the identification of minerals. • M
Many minerals have different colors
i
l h
diff
t l and some d
minerals' colors are identical to other minerals' colors. It is important to understand what causes color in minerals in order to understand this mineral property. 24
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EXAMPLES‐ QUARTZ
• Clear quartz is white or cloudy (milky quartz). Clear quartz is white or cloudy (milky quartz).
• Purple (Amethyst), • Pink (Rose Quartz), • Gray or brown to black (Smoky Quartz) are also common.
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QUARTZ
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Smoky Quartz
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QUARTZ
: Purple (Amethyst)
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AZURITE
• Color is azure, • deep blue or pale blue if found in small crystals or crusts. 29
OLIVINE
Color is a light near emerald green to the more
common pale
yellowish green; also found colorless, greenish
brown to black.
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CALCIUM‐PLAGIOCLASE
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SODIUM‐PLAGIOCLASE
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POTASSIUM‐FELDSPAR
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Streak
Streak is the color of a powdered mineral.
Streak can be different than color.
This is usually determined by running the mineral across a piece of unglazed porcelain called a streak plate (or just unglazed white tile found at p
( j
g
the hardware store).
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Example Streak
THE MINERAL HEMATITE
THE MINERAL GALENA
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Two minerals that have similar outward color may have different colors when powdered. • Hematite's streak is blood‐red,
streak is blood red
• Galena's streak is lead gray. • Hematite (pictured above) is probably the most well known example of streak with its completely surprising streak color. 36
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Luster: is the appearance of light reflected from a minerals surface.
Unique terms :
Dull Dull ‐‐ just a non‐
just a non‐reflective surface of any kind Earthy ‐‐ the look of dirt or dried mud Earthy Fibrous ‐‐ the look of fibers Fibrous Greasy ‐ the look of grease
Metallic ‐ the look of metals Pearly ‐‐ the look of a pearl (Ex. Sanbornite
Pearly the look of a pearl (Ex. Sanbornite )
Silky ‐ the look of silk
Waxy ‐ the look of wax 37
Luster
Metallic Luster
Waxy Luster
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Tenacity
• Tenacityy refers to a mineral’s resistance to breaking, bending, or otherwise being deformed.
A mineral may be brittle, easily broken or crushed to powder; 39
• malleable, easily hammered into thin sheets (such as copper or gold); • sectile,
sectile easily cut with a knife; easily cut with a knife
• flexible, easily bent without breaking and then staying bent; or • elastic, bending but resuming its original shape once pressure is released. 40
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Tenacity is particularly useful in telling some of the metallic minerals apart.
• Gold
Gold is malleable, is malleable
pyrite (and most other look‐a‐likes) is not.
• Gold is also sectile and – in thin sheets – flexible.
• Galena is brittle, while • platinum is malleable and sectile. 41
Minerals are grouped as: •
Silicate
•
Nonsilicate
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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
• The simple ions of Silicon and Oxygen tend to bond together to form a complex ion to form a complex ion
Silicate Anion (SiO4) 4‐
The Silicate Anion bond with other elements and form minerals
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Common Silicate minerals
• Quartz (SiO2)
• Feldspar Group (Orthoclase: potassium feldspar and
Plagioclase :sodium and calcium feldspar)
:sodium and calcium feldspar)
• Mica Group (Biotite is the common dark colored mica mineral
(Muscovite is the common light colored mica mineral)
• Amphibole Group (Hornblende is the most common)
• Pyroxene Group (Augite is the most common)
• Olivine (Forms small, rounded crystals with no cleavage)
• Clay minerals (Kaolinite, Illite, Montmorillonite, etc.)
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Nonsilicate minerals
Several major groups exist including:
Group
Mineral
Native Elements:
Gold, Copper, Diamond, Sulfur,
Graphite
Carbonates
Calcite, Dolomite
Oxides
Hematite, Magnetite, Chromite
Sulfides
Galena, Pyrite,
y
Chalcopyrite
py
Sulfates
Gypsum, Anhydrite
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Carbonates
Carbonates are among the most abundant nonsilicate minerals in the Earth's crust. The sedimentary rock LIMESTONE is composed of
carbonate minerals • The basic building block of carbonates is the carbonate ion
carbonate ion (CO3) 2‐
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Carbonates
The carbonate ion (CO
The
carbonate ion (CO32‐) can bond with a variety of ) can bond with a variety of
other ions to produce the carbonate minerals. The bonding with calcium to form the mineral calcite
(CaCO3). produces one of the most abundant of the non‐silicate
non
silicate minerals. minerals.
All carbonates have the property of dissolving easily in acidic water.
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These carbonate minerals form by • Precipitation from marine or freshwater • Secretion by organisms as shells or skeletons 48
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THE CLAY MINERAL GROUP
Clay minerals are the product of the chemical weathering of silicate minerals, especially the of silicate minerals, especially the
feldspars. The clay minerals are a part of a general but important group within the phyllosilicates that contain large percentages of water trapped between the silicate sheets. 49
SOME PROPERTIES of THE CLAY MINERALS
• They can absorb water or lose water from simple humidity changes. • When mixed with limited amounts of water, clays become plastic and are able to be molded and formed in ways that most people are familiar with as children's clay.
• When water is absorbed, clays will often expand as the water fills the spaces between the stacked silicate layers. 50
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• Due to the absorption of water, the specific gravity of clays is highly variable and is lowered
with increased water content.
• The hardness of clays is difficult to determine due to the microscopic nature of the crystals, but actual hardness is usually between 2 ‐ 3 and many clays give a hardness of 1 in field tests.
• Clays
Clays are rarely found separately
are rarely found separately and are usually and are usually
mixed not only with other clays but with microscopic crystals of carbonates, feldspars, micas and quartz. 51
Clay minerals are divided into four major groups:
• The Kaolinite Group
The Kaolinite Group
• The Smectite Group (Montmorillonite)
• The Illite (or The Clay‐mica) Group
(
y
)
p
• The Chlorite Group
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Ore minerals
Some of the most important ore minerals and the metals extracted from them
Metal
Minerals
Iron
Hematite, Magnetite
Copper
Chalcopyrite, Native copper Aluminum
Bauxite
Gold
Native gold, Pyrite
Silver
Native silver
Native silver
Lead
Galena
Zinc
Sphalerite
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Rock Stability
Minerals which form at:
• high temperatures and pressures are least stable, and weather most quickly
• lower temperatures and pressures are most stable. 54
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Texture of Rocks
• SMALL CRYSTALS --------- COOLED
QUICKLY
(because of the reduced time for atoms to
attain minimum energy configuration)
• BIG CRYSTALS ------------- COOLED
SLOWLY
g may
y be so rapid,
p , as in a volcanic
• Cooling
eruption, that no crystalline structure
develops before solidification:
and an amorphous material such as
obsidian (volcanic glass) is formed.
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Bowens reaction series
Each mineral is more stable than the one
above it on the list.
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