IDENTIFICATION OF ROCKS AND MINERALS.pdf

FACULTY OF CIVIL & ENVIRONMENTAL ENGINEERING DEPARTMENT OF GEOTECHNICAL & TRANSPORTATION ENGINEERING ENGINEERING GEOLOGY & GEOPHYSIC LABORATORY REPORT SUBJECT CODE

BFC 21303

TEST CODE & TITLE

LAB 1 – IDENTIFICATION OF ROCKS AND MINERALS

COURSE CODE

BFF

TESTING DATE

3 JANUARY 2011

STUDENT NAME

MUHAMMAD RIDHWAN BIN KAMARUDIN (DF100038)

SECTION/GROUP

SECTION 1

GROUP MEMBER NAMES

1. MUHAMMAD IKHWAN BIN ZAINUDDIN (DF100018) 2.MUHAMMAD ZAMIR BIN SAMEON (DF100065) 3.MUKHLIS BIN ADAM (DF100080) 4. MUHAMMAD NUH BIN AHMAD ZAIRI (DF100093) 5. HANISAH BINTI HAMZAH (DF100052)

LECTURER/ INSTRUCTOR/

IR. AGUS BIN SULAEMAN

TUTOR NAME REPORT RECEIVED DATE

17 JANUARY 2011

MARKS

ATTENDANCE,

/15%

DISCIPLINE & INVOLVEMENT

EXAMINER COMMENT

DATA ANALYSES

/20%

RESULT

/20%

DISCUSSION

/25%

CONCLUSION

/20%

TOTAL

/100% RECEIVED STAMP

1.0

TOPIC : IDENTIFICATION OF MINERALS (LAB 1A)

1.1

OBJECTIVE To familiar with the physical properties of minerals in laboratory by hand.

1.2

LEARNING OUTCOMES Students should able to identify various specimens of mineral by physical testing. Students should able to identify minerals content in rock formation.

1.3

THEORY Each mineral possesses certain physical properties or characteristics by which it may be recognized or identified. Some are subjected to certain simple tests. Physical properties are useful in mineral identification. A mineral can be defined as a natural inorganic substance having a particular chemical composition or range of composition, and a regular atomic structure to which its crystalline from is related. To study rocks, it is necessary to know the rock forming minerals.

1.4

EQUIPMENT AND MATERIALS a) Minerals from Reference Set b) Hardness Pens Set c) Information & Hints d) Eye dropper bottle with dilute HCI (appx. 10% solution) e) Mineral Identification Chart

1.5

PROCEDURE Students should learn to familiarize and observe the samples according by doing few physical tests and tabulate the results from the observation in the Table 1.1 attached for:

a) b) c) d) e) f) 1.6

Name of mineral Colour Luster Hardness Reaction with acid Others/usage

RESULT AND ANALYSIS 1.6.1 MINERALS NAMES Refer to the samples prepared (Mineral from reference set). 1.6.2 COLOUR The colour of the mineral is that seen by eye. Colour may be influenced by impurities in the sample, the light in the room or strong reflective surfaces. Therefore, colour is a general rather than specific indicator. 1.6.3 STREAK Streak is the colour of a mineral in its powdered form. We can observe streak when we scraped a mineral along a roughened surface such as unglazed pottery (porcelain slab – streak plate), that mark left behind can be a characteristic feature of the mineral. The streak is not necessarily the same as the colour of the mineral.

1.6.4 LUSTRE Luster is reflected from the surface of a mineral, the amount of light is a function of the state of the surface. Luster is described in terms of the degree of brightness.

Metallic

Like polished metal

Submetallic

Less brilliant

Dull

e.g. chalk

Viterous

Like broken glass

1.6.5 HARDNESS The resistance of a mineral to abrasion (scratching) is termed hardness. This property is determined by rubbing the mineral to be identified against another mineral of known hardness. One will stretch the other (unless they have the same hardness). Geologists used a standard hardness scale, called the Mohs scale developed by German Mineralogist Friedrich Mohs (1773 – 1839) which assigns relative hardnesses to several common and a few rare and precious minerals as given below.

1.6.6

Relative hardness

Minerals

Mineralogy

10

Diamond

Carbon

9

Corundum

Alumina

8

Topaz

Aluminium silicate

7

Quartz

Silica

6

Feldspar

Alkali silica

5

Apatite

Calcium phosphate

4

Fluorite

Calcium fluoride

3

Calcite

Calcium carbonate

2

Gypsum

Hydrated calcium sulphate

1

Talc

Hydrated magnesium silicate

REACTION WITH ACID When dilute hydrochloric acid (typically 10%) is capped on to some minerals a reaction takes place. On calcite (CaCO3) bubbles of carbon dioxide are produced, in some iron sulphide ores, hydrogen sulphide is produced.

1.7

QUESTION AND DISCUSSION Briefly describe and explain two (2) classifications for each type Mineral are classified on their chemistry, particularly on the anionic element or polyanionic group of element that occur in the mineral. An anion is a negatively charge atom, and a polyanion is strongly bound group of atoms consisting of a cation plus several anions (typically oxygen) that has anet negative charge. This classification has been successful because mineral rarely contain more than one anion or polyanion, whereas they typically contain several different cations.

Silicate Mineral  A group of minerals contains SiO444- as the dominant polyanion. In these minerals the Si4+ cation is always surrounded by 4 oxygen in the form of a tetrahedron.  Because Si and O are the most abundant elements in the Earth, this is the largest group of minerals and is divided into subgroups based on the degree of polymerization of the SiO4 tetrahedra.  Silicate minerals are complex in both chemistry and crystal structure but every silicate minerals contains a basic structural unit called the silica tetrahedron with crystal structure.  Approximately 30% of all minerals are silicates and some geologist estimate that the crust has been about 95% silicate minerals, of which some 60% is feldspar and 12% quartz.  Silicate classification is based on the following types of linkage :i) Single chains – pyroxene ii) Double chains – amphiboles iii) Two dimensional sheets minerals – micas, chlorites & clay minerals iv) Three dimensional frameworks – feldspar and quartz. Non Silicate Minerals  The non-silicate minerals are those minerals that do not contain silica tetrahedron. These minerals are generally can be classified as :i) Oxides and Hydroxides ii) Carbonates and Sulfates iii) Halides

1.8

CONCLUSION Base on our result, there have its significance of mineral samples in construction industry. Minerals and rock are important especially to civil engineers because in designing any new structures or underground works, engineers must be able to evaluate and distribute natural minerals present at site to incorporate during the design stage and chemicals characteristic or minerals and rock that make up the Earth’s crust. Beside that, knowledge of minerals is essential for engineers who deals with earth materials since minerals are partially responsible for the physical and mechanical properties of rock and soils encountered in mines, tunnels, opencasts and excavation. As a result, from the experiment we can identify the physical properties of minerals where it is very useful in minerals identification. It is necessary to study the minerals before get to now rocks.

TABLE 1.1 STREAK

PHYSICAL PROPERTIES OF MINERALS IDENTIFICATION LUSTER HARDNESS REACTION WITH ACID

NAME

COLOUR

Copper Ore (Chacopyrite)

Gold

Olive Grey 5Y 4/1

Submetallic

5

Graphite

Silver

Med. Light Grey

Metallic

2

Garnet

Dark Chocolate Brown

Pale Yellowish Brown 10YR 6/2

Submetallic

9

Hornblende (Amphibole)

Black

Greenish Grey 5GY 6/1

Metallic

4

Zinc Ore (Sphalerite)

Dark Brown

Greyish Yellow 5Y 8/4

Metallic

3

SKETCH

Iron Ore (Hematite). Ferric Oxide

Grey Silver

Moderate Brown 5YR 4/4

Submetallic

8

Iron Ore (Limonite)

Orange + yellow

Dark Yellowish Orange 10YR 6/6

Dull

4

Talc

White Metallic

White

Submetallic

2

Microclime (“Orthoclase”)

Peach

White

Submetallic

6

Aluminium Ore (Bauxite)

Light Brown

Very Pale Orange 10YR 8/2

Dull

4

2.0

TOPIC : IDENTIFICATION OF IGNEOUS ROCK (LAB 1B)

2.1

OBJECTIVE To recognize, identified and observed distinguishing features of igneous rock specimen in the laboratory.

2.2

LEARNING OUTCOMES a) Students should able to recognize types of igneous rock formation in Malaysia and Worldwide. b) Students should able to evaluate the physical properties of igneous rocks for civil engineering application. c) Students should able to understand igneous rock forming on the earth.

2.3

THEORY a) Criteria for distinguishing igneous rock In describing any rock, one should proceed from the general to the particular, nothing firstly its colour, behaviour on weathering and any other striking features and then deciding whether it is igneous or other types of rock. The outstanding characteristics of the igneous rocks is given below, but must be emphasized that one characteristic by itself proof positive that the rock belongs to a certain class. Rock Type Igneous

b) c)

Characteristic Interlocking grains, massive structures Texture such as glassy, prophyritic, phaneritic, aphantic High feldspar or ferromagnesian content Absent of stratification or fossils

Description Physical characteristics Structure

Colour Massive – rock is uniform in appearance showing no banding or other structural features Pegmatite – the rock is very coarse grained Vesicular – the rock contains many cavities Crystallinty or degree of crystallization Holocrystalline – wholly crystalline Hemicrystalline – partly crystals and partly glass Holohyaline – wholly glass

Texture Granularity, the size of crystals Fine-grained when particles are 1 mm or less in diameter Medium grained when particles are 1 – 5 mm or more in diameter Coarse grained when the particles are 5 mm or more in diameter

2.4

EQUIMENT AND MATERIALS a) Igneous rock from reference set b) Igneous classification chart

2.5

PROCEDURE Students should learn to familiarize and observe the samples by referring the igneous classification charts and tabulate the results observation in the Tables 1.2.1 attached.

2.6

RESULT AND ANALYSIS a) Rock name b) Texture c) Colour d) Mineral composition e) Chemical composition f) Origin g) Sketch / Others

2.7

QUESTION AND DISCUSSION 1. Briefly explain two (2) types of igneous rock There are various ways of classifying igneous rocks. The most significant are mineralogical and chemical composition and rock texture (geological environment). Igneous rock are either formed Intrusive and Extrusive Rocks. Intrusive Rocks Intrusive igneous rocks are formed from magma that cools and solidifies within the crust of a planet. Surrounded by pre-existing rock (calledcountry rock), the magma cools slowly, and as a result these rocks are coarse grained. The mineral grains in such rocks can generally be identified with the naked eye. Extrusive Rock Extrusive igneous rocks are formed at the crust's surface as a result of the partial melting of rocks within the mantle and crust. Extrusive Igneous rocks cool and solidify quicker than intrusive igneous rocks. Since the rocks cool very quickly they are fine grained. 2. Explain the igneous rock classification according to the texture and chemical and mineral composition. Textural criteria are less critical in classifying intrusive rocks where the majority of minerals will be visible to the naked eye or at least using a hand lens, magnifying glass or microscope. Plutonic rocks tend also to be less texturally varied and less prone to gaining structural fabrics. Textural terms can be used to differentiate different intrusive phases of large plutons, for instance porphyritic margins to large intrusive bodies, porphyry stocks and subvolcanic dikes. Mineralogical classification is used most often to classify plutonic rocks. Chemical classifications are preferred to classify volcanic rocks, with phenocryst species used as a prefix, example "olivine-bearing picrite" or "orthoclase-phyric rhyolite". Igneous rocks can be classified according to chemical or mineralogical parameters. Chemical with total alkali-silica content for volcanic rock classification used when modal or mineralogic data is unavailable:     

acid igneous rocks containing a high silica content, greater than 63% SiO2 (examples granite and rhyolite) intermediate igneous rocks containing between 52 - 63% SiO2 (example andesite and dacite) basic igneous rocks have low silica 45 - 52% and typically high iron - magnesium content (example gabbro and basalt) ultrabasic igneous rocks with less than 45% silica. (examples picrite and komatiite) alkalic igneous rocks with 5 - 15% alkali (K2O + Na2O) content or with a molar ratio of alkali to silica greater than 1:6. (examples phonolite and trachyte)

An idealized mineralogy (the normative mineralogy) can be calculated from the chemical composition, and the calculation is useful for rocks too fine-grained or too altered for identification of minerals that crystallized from the melt. For instance, normative quartz classifies a rock as silica-oversaturated; an example is rhyolite. A normative feldspathoid classifies a rock as silica-undersaturated; an example is nephelinite.

2.8

CONCLUSION From our observation of the igneous rock in the laboratory, it is also having significance in construction industry. The geologist and the engineers working on projects have to determine the origin of the igneous rock and the mineralogy of the rocks. A rock which originated as molten magma from beneath the earth’s surface and subsequently came to the surface as an extrusion, or remained below ground as an intrusion. The nature of the rock depends in part on the rate at which it cooled; as intrusions of magma slowly solidify, enough time elapses for large crystals to form whereas extrusions cool quickly, leaving little time for crystal growth. Thus, a coarse-grained, intrusive igneous rock has a fine-grained, extrusive counterpart; granite is coarse rhyolite and gabbro is coarse basalt. Igneous rocks are also classified as acid or basic, according to whether their silica content is high (e.g. granite), or low (e.g. basalt). Igneous rock is formed through the cooling and solidification of magma or lava. Igneous rock may form with or without crystallization, either below the surface as intrusive ( plutonic ) rocks or on the surface as extrusive ( volcanic ) rocks. This magma can be melting is caused by one or more three processes : an increase in temperature, a described, most of them having formed beneath the surface of Earth’s crust. These have diverse properties, depending on their composition and how they were formed.

TABLE 1.2.1 ROCK NAME

TEXTURE

COLOUR

Obsidian

Aphanitic, even or porphyritic

Light < 25% mineral dark

Rhyolite

Aphanitic, even or porphyritic

Light < 25% mineral dark

Biotite – Granite

Medium to coarse phaneric

Light < 25% mineral dark

IDENTIFICATION OF IGNEOUS ROCK MINERAL COMPOSITION

Hornblande, Biotite, Most Covite, Orthoclase, Quarts

Hornblande, Biotite, Most Covite, Orthoclase, Quarts

Hornblande, Biotite, Most Covite, Orthoclase, Quarts

CHEMICAL COMPOSITION

ORIGIN

Asid > 65%

Plutonic

Asid > 65%

Plutonic

Asid > 65%

Volcanic

SKETCH

Hornblende Syenite

Medium to coarse phaneric

25% - 50% dark mineral

Basalt

Aphanitic, even or porphyritic

Park minerals precominant

Gabbro

Medium to coarse phaneric

Park minerals precominant

Hornblande, Orthoclase, Plagioclase Biotite, Magnatic & Ilmenite

Hornblande, Augite, Plagioclase, Olivine, Magnatic & Ilmenite

Hornblande, Augite, Plagioclase, Olivine, Magnatic & Ilmenite

Intermediate 55% 65%

Volcanic

Basic 45% - 55%

Volcanic

Basic 45% - 55%

Plutonic

IGNEOUS CLASSIFICATION CHART

3.0

TOPIC : IDENTIFICATION OF SEDIMENTARY ROCK (LAB 1C)

3.1

OBJECTIVE To recognize, identified and observed distinguishing features of sedimentary rock specimen in the laboratory.

3.2

LEARNING OUTCOMES a) Students should able to recognize types of sedimentary rock formation in Malaysia and Worldwide. b) Students should able to evaluate the physical properties of sedimentary rocks for civil engineering application. c) Students should able to understand sedimentary rock forming on the earth.

3.3

THEORY (a) Criteria for distinguishing sedimentary rock In describing any rock, one should proceed from the general to the particular, nothing firstly its colour, behaviour on weathering and any other striking features and then deciding whether it is sedimentary or other types of rock. The outstanding characteristics of the sedimentary rocks is given below, but must be emphasized that one characteristic by itself proof positive that the rock belongs to a certain class.

Rock Type

Sedimentary

Characteristic Stratification and sorting of grains into layers according to their size. Fragmental texture. Grains often rounded. Structures such as bedding, ripple marks and mud cracks. Presence of fossils. Presence of minerals of chemical or organic origin, such as halite, gypsum, chert carbonates. Absence of easily weathered minerals such as biotite and augite.

(b) Description Physical characteristics Structure Grain and constituents

3.4

Colour Massive, bedded or cross bedded Note whether grain is uniform or uneven. To be uneven, there must be marked contras between larger and smaller grains. If the rock is uniform, it is usually fine in grain and does not show definite fragments, but may contain fossils.

EQUIMENT AND MATERIALS a) Sedimentary rock from reference set b) Sedimentary classification chart

3.5

PROCEDURE Students should learn to familiarize and observe the samples by referring the sedimentary classification charts and tabulate the results from the observation in the Table 1.2.2 attached.

3.6

RESULT AND ANALYSIS a) Rock name b) Texture c) Mode of origin d) Composition of clastic rock e) Composition of crystalline rock f) Sketch / others

3.8

QUESTION AND DISCUSSION 1. List the characteristics that distinguish sedimentary rocks from igneous and metamorphic rocks. Sedimentary rocks from by accumulation of sediment grains or by biologic or chemical precipitation from liquid water. Igneous rocks from by crystallization of a magma. No magma needs to be present for metamorphic crystallization. 2. Explain all the genesis of sedimentary rocks. Sedimentary rocks form at the Earth’s surface through interactions of the hydrologic system and the crust. Fortunately, many of these processes are in operation today, and geologists actively study rivers, deltas and oceans of all parts of the Earth. This research indicates that the genesis of sedimentary rocks involves four major processes: i. Weathering is the interaction between the elements in the atmosphere and the rocks exposed at the Earth’s surface. This process can take place chemically or physically. ii. Transportation is done mostly by running water. However, glaciers and wind can also transport sediment, although their activity is somewhat restricted to special climate zones. Sorting that occurs during transportation is an important factor in the genesis of sedimentary rocks. This sorting is according to both size and composition, and the entire sorting process is referred to as sedimentary differentiation. iii. Deposition occurs in a specific sedimentary environment. This environment reflects the physical, chemical and biological conditions that exist at the place of deposition. Distinctive types of texture, composition, internal structure, and fossil assemblages are developed in each environment. The environments include continental, marine and shoreline. iv. Compaction and Cementation transforms the loose, unconsolidated sediment into solid rock. The weight of continually accumulating material helps compress and compact the buried sediment into rock. Cementation occurs as mineral matter, carried by water seeping through the pore spaces of tight grains, is precipitated. Cements are commonly made of quartz, calcite or limonite.

3.9

CONCLUSION Based on our experiment for the sedimentary rocks, we found that well-cemented sedimentary rocks generally adequate for most type of building foundations. Special problems occur in lime stones and evaporate deposits because these rocks are soluble under the action of following groundwater. The soils and rocks overlying underground cavities produced by chemical dissolution may collapse into voids, damaging or destroying building constructed at the surface. The most unfavorable situation occurs were bedding dips in down slope direction of a slope or excavation. Bedding planes are zones of weakness sedimentary rock masses and failure may occur. Tunneling and underground mining in sedimentary rocks are influenced by lithology and structure (orientation of bedding). In slope construction, stable vertical slopes can usually be excavated in wellcemented, horizontally bedded sandstone and limestone. Flatter slope angles must be cut for weaker rock types. A particularly important factor in the stability of sedimentary rock slopes is the direction and amount of slope or dip of bedding. From our research, we found the certain of their significance in construction industry such as conglomerate is a sedimentary rock with a variable hardness consisted of round or angular or mineral fragment cemented by silica, lime, iron oxide and etc. usually found in mostly thick, crudely stratified layers. Used in the construction industry. For the third sample is argillaceous shale which it is well stratified in thin beds. It splits unevenly more or less parallel to bedding plane and may contain fossils. It can be a component of bricks and cement. For our forth sample is limestone where it is used mainly in the manufacture of Portland cement, the production of lime, manufacture of paper, fiberglass, glass and as the coating on many types of chewing gum.

TABLE 1.2.2

IDENTIFICATION OF SEDIMENTARY ROCK COMPOSITION MODE OF ORIGIN CLASSIFICATION OF ROCK

ROCK NAME

TEXTURE

SHELL LIMESTONE

Medium Grained 1 / 16 – 2mm

Mechanical or Bioclastic

DOLOMITIC LIMESTONE

( 1 / 256 – 1 / 16 mm ) Fine – Grained < 1 / 256 mm

Mechanical or Bioclastic

ARGILLACEOUS SHALE

( 1 / 256 – 1 / 16 mm ) Fine – Grained < 1 / 256 mm

Mechanical or Bioclastic

Quartz and feldspar Clayey, silty, sandy, Ferruginous Not common

Clastic Rock

BITUMINOUS COAL

Coarse – Grained ( > 2mm )

Mechanical or Bioclastic

Altered plant material

Clastic Rock

Shell Clayey, silty, sandy, Calcareous, carbonaceous, Calcareous phospatic

Shell Clayey, silty, sandy, Calcareous, carbonaceous and phospatic

Clastic Rock

Clastic Rock

SKETCH

ROCK NAME

TEXTURE

CHERT

Coarse ( > 2mm ) Medium ( 1/16 to 2mm ) Fine ( < 1/16mm )

COMPOSITION OF ROCK

CLASSIFICATION

Hidrogenic, biochemical or chemically altered

Siliceous

Crystalline Rock

Mechanical or Bioclastic

Quartz and feldspar Clayey, silty, sandy, Ferruginous Not common

Clastic Rock

MODE OF ORIGIN

CONGLOMERATED ( Breccia if angular )

Coarse – Grained ( > 2mm )

RED SANDSTONE

Medium Grained 1 / 16 – 2mm

Mechanical or Bioclastic

Quartz Clayey, silty, sandy, Ferruginous Siliceous, ferruginous calcareous

Medium Grained 1 / 16 – 2mm

Mechanical or Bioclastic

Quartz Clayey, silty, sandy, Ferruginous Siliceous, ferruginous calcareous

ARGILLACEOUS SANDSTONE

Clastic Rock

Clastic Rock

SKETCH

SEDIMENTARY CLASSIFICATION CHART

4.0

TOPIC : IDENTIFICATION OF METAMORPHIC (LAB 1D)

4.1

OBJECTIVE To recognize, identified and observed distinguishing features of metamorphic rock specimen in the laboratory.

4.2

LEARNING OUTCOMES a) Students should able to recognize types of metamorphic rock formation in Malaysia and Worldwide. b) Students should able to evaluate the physical properties of metamorphic rocks for civil engineering application. c) Students should able to understand metamorphic rock forming on the earth.

4.3

THEORY (a) Criteria for distinguishing sedimentary rock In describing any rock, one should proceed from the general to the particular, nothing firstly its colour, behaviour on weathering and any other striking features and then deciding whether it is metamorphic or other types of rock. The outstanding characteristics of the metamorphic rocks is given below, but must be emphasized that one characteristic by itself proof positive that the rock belongs to a certain class. Rock Type Metamorphic

Characteristic Parallel orientation of mineral crystals. Interlocking crystal. Secondary cleavage independent bedding. Foliation, schistosity and slaty texture.

(b) Description Physical characteristics Structure and Grain

Colour Decide whether the rock is best described as uniform fine grained, medium fine grained or coarse grained. The coarser grained granular rocks results from high-grade metamorphism in which great pressure from many directions, not from one direction only, has been the dominant factor.

4.4

EQUIMENT AND MATERIALS a) Metamorphic rock from reference set b) Metamorphic classification chart

4.5

PROCEDURE Students should learn to familiarize and observe the samples by referring the metamorphic classification charts and tabulate the results from the observation in the Table 1.2.3 attached.

4.6

RESULT AND ANALYSIS a) Rock name b) Structure c) Grain d) Mineral composition e) Parent Rock f) Metamorphism type g) Sketch / Others

4.7

QUESTION AND DISCUSSION 1. What is foliation? Foliation is any penetrative planar fabric present in rocks. Foliation is common to rocks affected by regional metamorphic compression typical of orogenic belts. Rocks exhibiting foliation include the typical sequence formed by the prograde metamorphism of mudrocks; slate, phyllite, schist and gneiss. The slatey cleavage typical of slate is due to the preferred orientation of microscopic phyllosilicate crystals. In gneiss the foliation is more typically represented by compositional banding due to segregation of mineral phases. Foliated rock is also known as S-tectonite in sheared rock masses. 2. Distinguish between slaty cleavage, phyllitic, schistosity and gneissic texture. i. Slaty Cleavage - This texture is caused by the parallel orientation of microscopic grains. The name for the rock with this texture is slate, and the rock is characterized by a tendency to separate along parallel planes. This feature is a property known as slaty cleavage. ii. Phyllitic Texture - This texture is formed by the parallel arrangement of platy minerals, usually micas that are barely macroscopic. The parallelism is often silky, or crenulated. The predominance of micaceous minerals imparts a sheen to the hand specimens. A rock with a phyllitic texture is called a phyllite. iii. Schistose Texture - This is a foliated texture resulting from the suhparallel to parallel orientation of platy minerals such as chlorite or micas. Other common minerals present are quartz and amphiholes. A schistose texture lies between the parallel platy appearance of phyllite and the distinct banding of gneissic texture. The average grain size of the minerals is generally smaller than in a gneiss. A rock with schistose texture is called a schist. iv. Gneissic Texture - This is a coarsely foliated texture in which the minerals have been segregated into discontinuous hands, each of which is dominated by one or two minerals. These bands range in thickness from 1 mm to several centimeters. The individual mineral grains are macroscopic and impart a striped appearance to a hand specimen. Light-colored bands commonly contain quartz and feldspar. and the dark hands are commonly composed of hornblende and hiotite. Accessory minerals are common and are useful in applying specific names to these rocks. A rock with a gneissic texture is called a gneiss.

4.8

CONCLUSION Metamorphic rocks form from heat and pressure. Some of the minerals that make up those rocks also change properties as heat and pressure is applied. Polymorphs of minerals at different phases result and thus some minerals are only found in metamorphic rocks. From our observation of the metamorphic rock, it can be divided into two types of foliation. There are foliated and non-foliated metamorphic rocks. None foliated metamorphic rock posses similar engineering properties to igneous rocks. In an unaltered and unfractured condition, they can be considered to be strong materials, with few limitations for foundations, tunnels and dams. In a way similar to the igneous and sedimentary rocks, the behavior of metamorphic rock mass depends upon the degree and orientation of fractures the weathering characteristics. There properties must be curtained prior to construction of each individual engineering project. In construction industry, the significance of metamorphic rock such as some schist’s has graphite and some are use as building stones. Besides that, gneiss is due to physical and chemical similarity between many gneisses and plutonic igneous rocks some are used as building stones and other structural purposes.

TABLE 1.2.4

IDENTIFICATION OF METAMORPHIC ROCK

ROCK NAME

STRUCTURE

GRAIN

MINERAL COMPOSITION

Gneiss

Gneissic

Medium to coarse

Quartz, Feldspar, Minor, Ferromagnesians

PARENT ROCK

METAMORPHISM TYPE

Granite, Arkose, Conglomerate.

Regional

Shale, Mudstone or tuff

Increasing Regional

Mica Schist

Schistose

Medium to coarse

Micas, Quartz, Feldspar,

Quartzite

Granulose

Medium to coarse

Quartz greatly predominant

Quartz, Sandstone

Regional

Shale, Mudstone tuff

Dynamic

Limestone

Contract of regional

Slade

Cleared

Very fine

Clay mineral, Detrital micas, Chlorite

White Marble

Granulose

Medium to course

Calcite of dolomite greatly dominant

SKETCH

METAMORPHIC CLASSIFICATION CHART