Title: A BRIEF STUDY OF MINERALS
1A BRIEF STUDY OF MINERALS
- Presented by Linder Winter
- 2005 Hammond Coaches Clinic
2A BRIEF STUDY OF MINERALS
- Note The mineral numbers used throughout this
presentation refer to the specimen numbers of the
minerals in the ESES mineral set referenced in
the Rocks and Minerals Event Rules of the
National Science Olympiad.
3A BRIEF STUDY OF MINERALS
- This presentation is divided into three parts
Environments of Formation, Identification of
Mineral Shapes, and Identification of Minerals.
4A BRIEF STUDY OF MINERALS
- Part I Environments of Formation
5Minerals and Crystals
- Whether a given mineral soup forms into random
aggregates of grains within commonly found rocks
or beautiful crystals, both are similar in
composition. - This presentation approaches the study of
minerals and their crystalline forms as if they
are the same.
6Part I Environmentsof Crystal Formation
- Few minerals have a field of stability so
restrictive that they can crystallize in only one
type of environment. - The slides that follow describe the environments
of formation for many - of the minerals included on the official
National Science Olympiad list.
7Igneous Environments
- Numerous cavities and fractures are found deep
within the Earth where crust and mantle meet. It
is within these spaces where essen-tial
conditions for crystal growth are found. - Fluids composed of water, CO2, and volatiles
(substances that give off gasses) escape from
molten magma and flow through these fractures and
cavities.
8Igneous Environments
- These cavities and fractures provide the space
and the range in temperature and pressure
required for minerals to form. - Now all that is needed is time and lots of luck.
- Should the cavities close due to shifting of the
crust and mantle, crystal growth may cease. - Should the cavities reopen, volatiles with a
different composition may become available,
resulting in crystals of different shades of
color or even different minerals.
9Igneous Environments Hydrothermal
- Hydrothermal, as the name implies, involves water
and heat. - As water percolates through the lower portion of
Earths crust, it dissolves minerals released
from magma. - These hydrothermal fluids move through fractures
in the crust. Along the way, they dissolve
additional minerals, or combine with other ground
water. If combined with the right combination of
temperature, pressure, time, and space, crystals
may form.
10Igneous Environments Pegmatite Dikes and Veins
- Large masses of concentrated volatiles may form
as isolated floating globs within the magma in
the upper part of the mantle. - These volatile-rich masses may eventually cool to
form pegmatite dikes and veins. - Many rare and beautiful minerals are produc-ed
within pegmatites topaz, beryl, corundum,
tourmalines, micas and apatite.
11Specific Minerals Associated with Igneous
Environments
- 1. Within slow-forming rocks during the principal
stage of crystallization of a body of molten rock
(magma) olivine, amphibole, mica, feldspars,
quartz, apatite, magnetite, diamond.
12Specific Minerals Associated with Igneous
Environments
- 2. Within hydrothermal veins formed in fissures
as a result of precipitation from solution
feldspars, quartz, epidote, barite, calcite,
hematite, fluorite, galena, sphalerite,
chalcopyrite, pyrite - 3. Within fumarolic deposits formed as a result
of sublimation of volcanic fumes hematite,
pyrite, sulfur
13Specific Minerals Associated withSedimentary
Environments
- Those associated with weathering of mineral
deposits malachite, azurite, gold, silver,
copper - Evaporation of water, especially sea water
gypsum, calcite, dolomite, halite - Activities of animal and vegetable organisms
sulfur, aragonite, apatite, bauxite, chalcedony
14Specific Minerals Associated with Metamorphic
Environments
- 1. Formed by solid-state transformation due to
temperatures and pressures often different from
the original mineral-forming ones. - 2. These solid-state minerals include garnets,
micas, staurolite, amphiboles (hornblende),
corundum, pyrite, graphite.
15II. Crystalline Shapes
- Identification of Crystalline Shapes
- Crystal images on the following slides are
- compliments of Wikipedia, The Free Encyclopedia
16Axis of Rotation
- An axis of symmetry is an imaginary line drawn
through the center of a crystal around which it
may be rotated so that each successive face
appears similar to the one preceding it. - Depending on the number of degrees through which
the crystal must be rotated to produce this
effect, a crystal may look the same from 2, 3, 4,
or 6 different positions such a crystal is
described as having n-fold symmetry (e.g.
"2-fold symmetry") along that axis of rotation.
17Identification of Crystalline Shapes
- Isometric or cubic three axes of symmetry, all
of equal length. - Envision an axis drawn from the center of the top
face to the center of the bottom face. - Envision the cube rotat-ed about that axis. A
total of four identically-shaped faces appear as
the cube rotates.
18Identification of Crystalline Shapes
- Imagine a second axis drawn from the center of
the left face to the center of the right face. - Rotate the cube on that axis. Four
identically-shaped faces will again rotate into
view.
19Identification of Crystalline Shapes
- Finally, imagine an axis drawn from the center of
the front face to the center of the rear face. - A cube displays four three-fold axes, i.e. four
similar faces for each of its 3 axes.
20Identification of Crystalline Shapes
- Tetragonal three axes of rotation, two of equal
length and a third that is either longer or
shorter. - Envision three axes of rotation, only one of
which is a four-fold axis. - Which of the axes of
- rotation in this crystal has a four-fold axis?
21Identification of Crystalline Shapes
- Which of the axes
- of symmetry in this crystal has a four-fold
axis? - The longest axis as the crystal rotates, four
similar-appearing faces appear in succession.
22Identification of Crystalline Shapes
- The other two axes are two-fold, i.e. as the
tetragonal crystal rotates about its axis, two
similar-appearing faces are alternately revealed.
23Identification of Crystalline Shapes
- Hexagonal four axes of rotation -- three of
equal length and a fourth that is either longer
or shorter. - One axis of six-fold symmetry
24Identification of Crystalline Shapes
- Orthorhombic three axes of rotation, each
- of unequal length.
- Two-fold symmetry
25Identification of Crystalline Shapes
- Monoclinic three axes of rotation each of
unequal length. - When viewed in the position shown, this object
has three axes of unequal length top to bottom
right to left front to back. - One two-fold axis the axis of symmetry.
26Identification of Crystalline Shapes
- Triclinic three axes of length, none
perpen-dicular to the other. - Three axes, all of unequal length, none at right
angles to the others. - No axes of symmetry
27Identification of Crystalline ShapesCoaching
Strategy
- Have participants construct their own models.
When completed, have them identify the number of
axes of rotation and the number of folds. - These models may be found at (Enter this URL in
your notebook letter case counts!) - http//bca.cryst.bbk.ac.uk/BCA/ed/Class.pdf
28III. Mineral Properties
29Luster Basics
- Luster is a subjective judgment indicating how a
mineral appears to reflect light. - A major distinction is whether a minerals luster
is metallic or nonmetallic. - Luster of non-metallic minerals may vary from
specimen to specimen. - Diagnostic properties reflect the internal
structure and composition of minerals.
30Earthy LusterDirt or Dried Mud Appearance
- Specimen 23A Goethite
- Specimen 31A Kaolinite
31Vitreous Luster Glass-Like
- Specimen 9A Barite
- Specimen 21A Fluorite
- A majority of specimens on the official NSO list
display a vitreous luster.
32Dull Luster Non-Reflective
- Specimen 29A Hematite
- Specimen 34A Malachite
33Pearly LusterPearl-Like
- Specimen 37A Opal
- Specimen 35A Muscovite
34Metallic LusterMetal-Like
- Specimen
- Silver
- Specimen 38A Pyrite
35Greasy LusterGreasy-Like
- Specimen 49A Sodalite
- Specimen 53A Talc
36Adamantine LusterBrilliant
- Specimen 50A Sphalerite
- Specimen 54A Topaz
37Resinous LusterSimilar to Resin or Sap
- Specimen 50A Sphalerite
- Specimen 52A Sulfur
38Silky LusterSilk-Like
- Specimen 56A Tremolite
- Specimen 57A Ulexite
39Mineral Properties
40Mohs Hardness Scale
- Many years ago, Fried-rich Mohs proposed his
Hardness Scale which is still in use today. - 1. Talc
- 2. Gypsum
- 3. Calcite
- 4. Fluorite
- 5. Apatite
- 6. Orthoclase
- 7. Quartz
- 8. Topaz
- 9. Corundum
- 10. Diamond
41Hardness Basics
- Hardness is the ability of a mineral to resist
scratching or abrasion. - Hardness is a very reliable physical property for
use in the identification of minerals due to
chemical consistency of minerals. - The hardest minerals tend to be those with small
atoms packed tightly together with strong
covalent bonds throughout.
42Hardness Basics
- Hardness among individual specimens of the same
mineral may vary slightly. - Inconsistencies occur when the specimen is
impure, poorly crystallized, or an aggregate of
the same crystal. - A scratch on a mineral is actually a groove
produced by micro-fractures on the surface of a
mineral.
43Hardness
- Minerals may be tested for hardness by scratching
one mineral of known hardness against another
whose hardness one wishes to determine. - To limit the damage to minerals, other
non-mineral objects of known hardness may be
substituted for those used to test others for
hardness.
44Hardness Test Basics
- Do not SCRATCH NICE CRYSTAL FACES! Test on
fractured, cleaved, or inconspicuous parts of a
mineral only. - Ideally, hardness tests should be performed on
only individual crystals. A massive system is
most likely to be softer.
45Hardness Test Hints
- Make certain a scratch is a scratch rather than a
dust trail left on a mineral after being
scratched by a softer material. This is
particularly true when testing harder minerals
against porcelain plates. - Most minerals have small differences in hardness
according to the direction and orientation of the
scratch.
46Hardness Test Precautions
- NEVER perform streak or hardness tests on
minerals unless specifically given permission by
the event supervisor to do so either verbally
or written! - Performing hardness tests causes harm to the
specimens. - The supervisor may provide scratch and/or
hardness test data in those instances when this
information would be helpful.
47Testing for Hardness
- Many of those event supervisors who do permit
hardness testing of their minerals provide
objects for participants for use as substitute
testing surfaces. - Fingernails 2.5
- Copper 3.5 (avoid pennies)
- Window glass 5.5
- Streak plate 6.5
48Determining Hardness
- Using fingernails, copper tubing, window glass,
and streak plate, determine the approximate
hardness of the following - Specimen 4A Apatite
- Specimen 17A Corundum
- Specimen 21A Fluorite
- Specimen 22A Galena
49Determining Hardness
- Apatite 5 Scratches copper (3.5), but
not glass (5.5) - Corundum 9 Scratches streak plate (6.5)
- Flourite 4 Scratches copper (3.5), but not
glass (5.5) - Galena 2.5 Scratches fingernail (2.5), but
not copper (3.5).
50Mineral Properties
51Streak Basics
- Streak is the color of a minerals powder.
- Streak, for a given mineral, is generally very
consistent from specimen to specimen thus making
it a valuable test for mineral ID. - A mineral harder than 6.5 will not leave a streak
on a streak plate due to the streak plates
hardness of 6.5. Be careful as a streak of
porcelain may result.
52Streak Basics
- Fortunately, most minerals with a hardness gt 6.5
have a white streak. - Streaks made by similarly-colored minerals may
differ from their outward surface color. - To test for streak, rub the mineral against a
tile of white, unglazed porcelain. - Note the color of the streak.
53Testing Various Specimens for Streak
54Testing Various Specimens for Streak
- Hematite leaves a dark red streak.
55Testing Various Specimens for Streak
56Testing Various Specimens for Streak
- Galena leaves a gray streak.
57Testing Various Specimens for Streak
58Testing Various Specimens for Streak
- Pyrite leaves a greenish black streak.
59Testing Various Specimens for Streak
60Testing Various Specimens for Streak
- Malachite leaves a light green streak.
61Testing Various Specimens for Streak
62Testing Various Specimens for Streak
- Barite leaves a white streak.
63Testing Various Specimens for Streak
- Chalcopyrite, Specimen 15A
64Testing Various Specimens for Streak
- Chalcopyrite leaves a dark green streak.
65Mineral Properties
66Fracture Basics
- Fracture describes how a mineral tends to break.
- Fracture differs from cleavage. Cleavage is the
tendency of some minerals to break along one or
more regular, smooth surfaces and will be
addressed later. - Fracture occurs in all minerals, even those with
cleavage.
67Fracture Basics
- Fracture is the way minerals break when they do
not yield along cleavage or parting surfaces. - Three commonly recognized fractures are
- 1. conchoidal smooth, shell-shaped
- 2. fibrous splintery
- 3. uneven rough and irregular
68Conchoidal Fracture
- Olivine 36A
- Magnetite 33A
- Conchoidal fracture is evident in the image of a
magnetite specimen.
69Uneven Fracture
- Hematite 29A
- Hornblende 30A
- Tremolite 56A
-
70Fibrous Fracture
71Mineral Properties
72Cleavage Basics
- Cleavage reflects the tendency of a mineral to
break along sets of parallel planes due to its
internal atomic structure having regular
directions of weaker bonding. - Cleavage planes fail when force is applied to
them. - The quality of cleavage may be described as
perfect, good, fair, or poor. - Not all minerals display cleavage.
73Cleavage Basics
- Cleavage is generally observable only in a
minerals crystal form, not in massive specimens.
74Determining Cleavage
- To determine whether a mineral specimen possesses
cleavage, ask yourself - Are there any sets of parallel planes along which
a mineral preferentially breaks? - If the mineral shows cleavage, how many different
sets of parallel planes does it have? - What are the approximate angles between the
different cleavage directions? 30 45
75Cleavage Test Precaution
- Do not confuse crystal faces planes formed by
the growth of a crystal with cleavages. - Crystal faces will not be sets of parallel
planes. They will be single surfaces.
76Biotite 11A
- Cleavage is perfect in one direction producing
thin sheets or flakes.
77Calcite 13A
- Cleavage is perfect in three directions forming
rhombohedrons.
78Galena 22A
- Cleavage is perfect in four directions forming
cubes.
79Halite 28A
- Cleavage is perfect in four directions forming
cubes.
80Mineral Properties
81Color Basics
- Silicon and aluminum rich minerals are typically
light in color quartz and feldspar. - Iron and magnesium rich minerals are typically
dark in color olivine and pyroxene.
82Color Basics
- Silicon and aluminum rich minerals are typically
light in color. - Iron and magnesium rich minerals are typically
dark in color. - Which of these minerals is most likely rich in
silicon and aluminum?
83Color Basics
- Which of these minerals is most likely rich in
silicon and aluminum ? - The feldspar in the upper photo is most likely
rich in silicon and aluminum.
84Color Basics
- Which of these minerals is most likely rich in
iron and magnesium? -
85Color Basics
- Which of these minerals is most likely rich in
iron and magnesium? - Both augite, in the upper photo and hornblende
in the lower photo are rich in iron and
magnesium. -
86Color Basics
- Caution!
- 1. Color can be altered by weathering.
- 2. Trace elements may alter the typical color
of a specimen. Generally, quartz is light in
color, but a small amount of iron may tint it a
purplish color. - 3. Some minerals come in a wide variety of
colors.
87Mineral Properties
88Transparency Basics
- Transparency describes the capability of a
mineral to transmit light. - A mineral can be transparent, translucent, or
opaque. - Most gem minerals are highly transparent.
- Most metallic minerals are opaque.
89Transparency Descriptions
- Three terms describe the full range of mineral
transparency - 1. Transparent light enters and exits in a
relatively undisturbed fashion - 2. Translucent light enters and exits, but in
a disturbed and distorted fashion - 3. Opaque light cannot penetrate the surface
90Transparency Test Precaution
- Effective for use with crystalline mineral forms
only!
91Halite 28A
- Is this specimen transparent,
- translucent,
- or opaque?
92Halite 28A
- Is this specimen transparent,
- translucent,
- or opaque?
93Calcite 13A
- Is this specimen transparent,
- translucent,
- or opaque?
94Calcite 13A
- Is this specimen transparent,
- translucent,
- or opaque?
95Topaz 54A
- Is this specimen transparent,
- translucent,
- or opaque?
96Topaz 54A
- Is this specimen transparent,
- translucent,
- or opaque?
97Amazonite 3A
- Are these specimens
- transparent, translucent,
- or opaque?
98Amazonite 3A
- Are these specimens
- transparent, translucent,
- or opaque?
99Mineral Properties
100Specific Gravity Basics
- Specific gravity is the density of a mineral
relative to that of water at 4C. It depends upon
the chemical composition and crystal structure of
the mineral. - Specific gravity has no unit because it is
derived from the density of the mineral divided
by the density of water. Thus, all units cancel. - A mineral with a SG of 2, is twice as dense as
water
101Specific Gravity Basics
- Earths crust, from where amateurs are most
likely to collect minerals, is composed mostly of
the minerals quartz, calcite, and feldspar. These
minerals have an average SG of 2.75. - Non-metallic minerals tend to be of low density
metallic minerals of high density.
102Testing for SG Hefting
- Hold a mineral of known SG in one hand and
another of unknown SG, of about the same size, in
the other. - Preferably, the mineral of known SG should be
near the average of 2.75. Compare the SG of the
known with the unknown.
103Testing for SG Hefting
- Chances are quite good that the event supervisor
will place three to four specimens at a station
and ask that these be ranked according to
specific gravity. - Because of the variability among the minerals in
the Science Olympiad kits, we will not perform a
specific gravity test by hefting during this
session.
104Testing for SG Lab Activity
- Important For the lab activity, be certain to
select only specimens containing one mineral. - Impure specimens containing significant amounts
of other minerals will result in incorrect
specific gravity values. - Supervisors may choose objects other than common
minerals, i.e. density blocks.
105Testing for SG Lab Activity
- Attach the mineral to a spring scale using a
length of string. - What is this minerals weight (D) in air?
- Suspend (totally immerse) the mineral in water.
- The letter W will represent the minerals weight
while suspended in water. - To calculate the minerals SG, use the formula
D/(D-W).
106Special Mineral Properties
- Some minerals may be easily identified due to
special properties
107Special Mineral PropertiesPenetration Twinning
- Staurolite is famous for its twinned crystals
that form into the shape of a cross. Staurolite
is an example of penetration twinning, the
symmetri-cal intergrowth of two or more crystals
of the same substance.
108Special Mineral PropertiesStriations
- Quartz, 44A striations are uniquely
perpendicular to the crystal length and appear
only on prism faces. - Pyrite, 38A Striations on one side of the cube
are perpendicular to the striations on the other
side.
109Striations Basics
- The most common cause of striations is the
convergence of two crystal faces. One of the
faces is overtaken by the other but manages to
leave its mark in the form of an almost
imperceptible edge, or stria. - This edging is repeated again and again as the
mineral grows and can fill an entire face with
these tiny edges or striations.
110Mineral Properties
111Form and Habit
- Geometric features of a single crystal may be
de-scribed in terms of crystal habit and crystal
form. - Crystal habit refers to the general shapes of
individual crystals or aggregates of crystals,
which are governed by the development of their
faces. - Crystal form refers to the characteristic
appearance of a crystal as determined by its
predominate form. - Common forms include cube, such as pyrite,
octahedron, such as fluorite, and hexagonal, such
as quartz.
112Form and Habit
- Copper provides a good example of crystal form
cubic. - Copper provides a good example of crystal habit
dendritic (similar in appearance to a river and
its tributaries).
113Form and Habit
- Halite has a cubic habit that reflects the cubic
arrange-ment of its atoms
114Form and Habit
- Mica has a sheet-like habit that reflects its
silicate sheet structure.
115Image Credits
- Credit has not yet been included for the images
appearing in this PPT presentation. We plan to do
this as soon as possible. We wish to thank those
individuals and organizations whose images appear
in this presentation. - This PPT presentation has been created for and
intended for use with students and teacher
work-shops. No profit is gained through this
presentation by any particular group or
individual. - This is a beta project. More time and effort will
be devoted to the improvement of this
presentation in the near future.