pe sc2015 practical 1-5

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620.010 and 620.002, Practical Introduction to Mineralogy and Petrology for PE 5/1

INTRODUTION TO MINERALOGY AND PETROLOGY

PRACTICAL 1

SUBJECT: MACROSCOPIC MINERAL IDENTIFICATION

I. CONCEPTAll minerals that are crystalline are characterised by a crystal lattice (“finger print” ofthe crystal/mineral). The crystal lattice is defined by i) the chemical components(atoms, ions, molecules), ii) by the chemical bonds, and iii) the 3-dimensionalsymmetrical order of the chemical components. All these three parameter of thecrystal lattice define all the physical and chemical properties of a crystal/mineral.The most important properties are:Crystal morphology (habitus = mode of growth, and crystal form), hardness, colour,streek colour, lustre, cleavage, elasticity, magnetic properties, density, and reactionwith acids.

II. TASKS

1. Complete the attached tables (Tables 1 and 2) by describing all the visiblemineral properties of the prepared mineral specimens.

2. Answer the additional questions.3. Try to identify the mineral specimens using the identification sheets attached.

1) SPECIMENS C and M! How can you describe the cleavage? Which different directions of cleavage

can you observe?! Are the minerals deformable elastically?! What is difference regarding color and lustre? Look also at thin platelets!

2) SPECIMEN M1! Try to draw one crystal!! Does this mineral have a cleavage? ?

3) SPECIMEN DThese are pieces of a larger crystal!

! Do you notice cleavage? In how many directions does cleavage occur?! What is difference to specimen M1 regarding color and lustre?

4) SPECIMEN M4! Is there a difference between the visible color and the streek color? If so, what

is the difference?! How can you describe the crystal morphology?

5) SPECIMEN G! Make the test with the hydrochloric acid! What can you observe?! How many directions of cleavage can you observe?! What is the hardness of this mineral?

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III. IMPORTANT MINERAL PROPERTIES FOR MINERALIDENTIFICATION – AN OVERVIEW

Crystal morphology (crystal habit)Morphological details are in most cases only visible when the particular

mineral/crystal is of decent size and “nicely” grown.Crystal form = the sum of geometric forms of a crystal (e.g. triagonal pyramide,prism, cube etc.). The crystal form is created, on the basis of the crystal lattice, duringcrystal growth. Crystal faces grow according to the symmetry of the crystal latticeand according to the space available. If there is not enough space available, so that allcrystal faces can grow regarding their individual pace of growth, the crystal will become distorted. Generally crystal growth is unlimited, only depending on thespace available and the physical-chemical conditions during crystal growth.

Habitus = is the growth shape of a crystal, i.e. whether it forms needles, growstabular, or isometric etc. Also the habitus is based on the crystal lattice.

Fracture behaviourCleavage = the way how a crystal breaks under mechanical force. If the crystal splitsalong one or more clearly defined directions, then the particular crystal showscleavage. In hand specimens cleavage commonly becomes visible by the plane smoothappearance and shiny lustre of the broken surface. The particular plane is calledcleavage plane. Cleavage planes develop when there are greatly varying bondingforces between the one or the other directions within the crystal lattice. If a crystalgets under mechanical force then equally charged ionic components of the latticecome to lie next to each other. The crystal will split exactly at that direction(s).Classification of cleavage:

! perfect! distinct! moderate! weak

Break of a crystal in irregular way = no cleavage can be observed, the minerals breaks irregularly. As a result the broken plane is not plane, smooth and shiny.

Density! low density (< 2.9 g/cm 3) – applies to many rock-forming minerals such as

quartz, feldspars, carbonates etc.! high density (< 2.9 g/cm 3) – applies to many ores such as oxides and sulfides.

Visible color (color in hand specimen)Color of a crystal/mineral is probably the most obvious property and aloscharacteristic for many minerals. Variations in the visible color of a mineral are inmost cases due to chemical impurities (e.g. smoky quartz, amethyst, ruby stone etc.).Therefore, one should be cautious to use visible color as the only characteristicproperty of a mineral.

Streek color = is defeined as the color of the mineral powder. It becomes obviouswhen skretching the particular specimen on a ceramic plate. The streek color isdefined as the “real” color of the particular mineral, and thus is in many casesdiagnostic for the mineral/crystal.

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LustreThe most diagnostic types of lustre are:

! metallic lustre! non-metallic lustre

Transparency =defines how much

of the incident light is refracted, absorbed, orreflected from the surface of the mineral. It is a function of the density of the

particular mineral. Following classification is used:

! non-transparent (= opaque)! translucent! transparent

HardnessOne of the most diagnostic properties of a mineral! It is determined using the Mohs´shardness scale . Practically applied via scratching one mineral against the other,observing carefully what is harder, what is softer!

Hardness Mineral of definition Scratching tools

1 Talc to scratch with the finger nail2 Gypsum to scratch with the finger nail3 Calcite to scratch with a copper coin4 Fluorite to scratch with a knife, glass5 Apatite to scratch with a knife, glass

6 Feldspar to scratch with a knife, glass7 Quartz8 Topas9 Corundum10 Diamond

Elasticity = the behaviour of a crystal/mineral during mechanical deformation

! brittle (feldspar, quartz)! ductile (muscovite, biotiite)

Other properties! Reaction with diluted hydrochloric acid – applied to distinguish between calcite

and other carbonate minerals, and carbonate from other minerals. Calcitereacts strongly with hydrchloric acid, dolomite shows weak reaction whenpowdered.

! Magnetic behaviour – Magnetite is the mineral with the strongest ferromagnetic behaviour.

! Taste – Halite tastes salty, other halides may taste bitter.

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Table 1

Specimen C Specimen M Specimen M1

Name

Habitus

Crystal form

Cleavage: direction(s)

Color in hand specimen

Streek color

Lustre

Hardness (Mohs scale)

Transparency

Density (relative to quartz)

Elasticity

Reaction with diluted HCl

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Table 2

Specimen D Specimen M4 Specimen G

Name

Habitus

Crystal form


Color in hand specimen

Streek color

Lustre


Transparency

Density (relative to quartz)

Elasticity

Reaction with diluted HCl

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INTRODUCTION TO MINERALOGY AND PETROLOGYPRACTICAL 2

SUBJECT: OXIDES and NESOSILICATES

Drawer 1Determine the prepared mineral specimens on the basis of the given macroscopicproperties on Tables 1 and 2. Be aware that not all properties might be existing, orpossible to observe!

1. What are the most significant differences between magnetite and chromite?

2. Why do magnetite and chromite have a high density?

3. What are the most significant differences between magnetite and hematite?

4. What are the characteristic properties of olivine?

5. Why is olivine the most abundant mineral within the Earth´s mantel?

6. What are the most significant properties of garnet?

Drawer II

7. Corundum : Which property is important for its industrial application?

8. Which minerals cause the rusty-brown weathering colour of many soils and surfacesof rocks?

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PRACTICAL 2 - Table 1Name Hematite Magnetite Chromite CorundumFormula

Crystal form

Habitus


Cleavage: quality

Color of hand specimen

Streek color

Lustre


TransparencytDensity (relative to quartz)

Elasticity

Other properties

Use

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Table 2 MU 622032 Übung 5 zu Einführung in der Mi

Name Ilmenite Goethite Olivine GarnetFormula

Crystal form

Habitus


Cleavage: quality


Streek color

Lustre



ElasticityOther properties

Use

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PRACTICAL 3 - Table 1 MU 622032 Übung 5 zu Einführung in der Mi

Name Amphibole Pyroxene Feldspar ZeoliteFormula

Crystal form

Habitus


Cleavage: quality


Streek color

Lustre




Use

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Table 2 MU 622032 Übung 5 zu Einführung in der Mi

Name Chlorite Serpentine Talc KaoliniteFormula

Crystal form

Habitus


Cleavage: quality


Streek color

Lustre




Use

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PRACTICAL 4 - Table 1Übung 7 zu Einführung in die Mineralogie und Petrologie

Name Aragonite Magnesite Siderite GypsumFormula

Crystal form

Habitus


Cleavage: quality


Streek color

Lustre



Elasticity

Other properties

Use

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Table 2 Übung 7 zu Einführung in die MineralogieName Baryte Galena Sphalerite ChalcopyriteFormula

Crystal form

Habitus


Cleavage: quality


Streek color

Lustre



Elasticity

Other properties

Use

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Tabelle 3 Übung 7 zu Einführung in die MineralogieName Fluorite Halite GraphiteFormula

Crystal form

Habitus


Cleavage: quality


Streek color

Lustre



Elasticity

Other properties

Use

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INTRODUTION TO MINERALOGY AND PETROLOGYPRACTICAL 5

SUBJECT: ROCK FABRICSTASK

Investigate the prepared rock specimens that represent typical examples of the 6principal rock fabric types. Draw a sketch of each typical rock fabric on the basis of yourobservations! Add a short summary of how these rock fabrics may have formed!

Fabric type specimen Petrogenetic interpretation

Sequentialcrystallisation

Vitric

Drusy

Granoblastic

Clastic

Deformed(Strained)

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SUBJECT: HOW TO DESCRIBE A ROCK? – A CHECK LIST

• Rock descriptions aim on (1) to facilitate the communication betweengeoscientists and engineers, so that each party knows what type of rock is subject;

(2) to stimulate thinking and interpretation on the basis of petrographicalobservations!

• Rock descriptions have to be based on observations. It represents the principaltool of geoscientists in order to document a hand specimen, a drill core, anoutcrop etc. The rock description sensu strictu always has to be separated fromthe interpretation! Rock descriptions based on profound observations is alwaysreproducable, whereas an interpretation involves the individual opinion of theobserver!

• In following a comprehensive check list is given in order to facilitate what to look

at when dealing with rocks!

1) Color: It is important to differentiate between the color of a fresh and a weatheredhand specimen, respectively.

2) Mineral composition: How many and which minerals can be observed? Describethe minerals following the way carried out during mineral description (e.g. color,cleavage, form etc.). Try to identify the minerals on the basis of characteristic

properties.3) Modal mineral composition: Estimate the modal % of each mineral observed and

identified.4) Grain-size:Look at the relative grain-size of the minerals identified in the rock.

Are there significant differences between the minerals, or are all the minerals ofalmost equal size?

5) Fabric: Describe and identify the fabric of the rock (i.e. according to the 6 principalfabric types).

6) Name: Give the rock a proper petrographical name based on its mineralcomposition and the fabric!

7) Petrogenesis: Think of how the particular rock has been formed, based on yourobservations! This is the interpretation!

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EXAMPLE OF A PETROGRAPHICAL DESCRIPTION OF A ROCK

Sample ÜP1General impression: fresh, unaltered (not weathered), grey, coarse-grained rock.

Mineralogy / Modal mineral composition:• ~15 % pink alkali-feldspar, euhedrally to subhedrally shaped, grain-size between 0.5

and 3 cm ø, bimodal grain-size distribution, smaller crystals dominate. Largecrystals show zonation. The smaller crystals occupy interstitial spaces between biotite and plagioclase.

• ~35 % dull white plagioclase, subhedrall, but dominantly anhedrally shaped crystalsof 0.5 and 3.0 cm in grain-size, bimodal grain-size distribution, smaller crystals

dominate.• Large crystals show zonation defined by a greenish core with many inclusions (most

likely biotite).• ~35 % glassy-grey quartz (0.5 - 1.5 cm ø);• ~10 % fine-grained, black platelets of biotite, grain-size between 0.1 and 0.5 cm. Tiny

little biotite inclusions are in all the other mineral components visible. Most of biotite, however, occurs in the immediate surrounding of the other mineral phases.

• Accessories:

pe sc2015 practical 1-5

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