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Study of Physical Properties of Minerals-II

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Study of Physical Properties of Minerals-II EXPERIMENT 5 STUDY OF PHYSICAL PROPERTIES OF MINERALS-II Structure________________________________________ 5.1 Introduction 5.7 Garnet Expected Skills 5.8 Kyanite 5.9 Nepheline 5.2 Requirements 5.10 Chlorite 5.3 Olivine 5.11 Epidote 5.4 Augite 5.12 Class Room Exercises 5.5 Hypersthene 5.13 Learning Resources 5.6 Hornblende 5.1 INTRODUCTION In the previous Experiment 4, you have identified the minerals belonging to feldspar and mica groups and quartz based on the physical properties. Similarly, in this experiment you will identify some rock forming minerals such as olivine, augite, hypersthene, hornblende, garnet, kyanite, nepheline, chlorite and epidote by studying their physical properties and diagnostic characteristics. You are advised to read the Section 4.3 of the previous experiment carefully to recall the physical properties for mineral identification. Expected Skills_____________________________________________ After performing this experiment, you should be able to: recognise the minerals in hand specimen based on their physical properties; identify some common rock-forming minerals like olivine, augite, hypersthene; 79 …………………………………BGYCL-134 ….…………………………………………………………………………………Crystallography, Mineralogy and Economic Geology:Laboratory recognise minerals like hornblende, garnet, kyanite, nepheline, chlorite, epidote; and learn about occurrence and uses of these minerals. 5.2 REQUIREMENTS You will require the following to perform this experiment successfully: Hand lens, pen knife, streak plate, coin, hardness box, glass plate Laboratory file, pen/ pencil and eraser Hand specimens of hornblende, garnet, kyanite, nepheline, chlorite, epidote, olivine, augite, hypersthene. Note: Do not use pen/pencil/marker pen to mark the hand specimen of the mineral. Please do not attempt to cleave the minerals in the laboratory. Many of the specimens you examine cannot be readily replaced. Do not break the mineral in order to see its cleavage. Cleavage is usually induced in the mineral when it is extracted from the rock it is found in, and is usually seen as planes running through the mineral. Instructions: You are required to study Units 4, 5 and 6 of BGYCT-133 course (Crystallography, Mineralogy and Economic Geology) before performing this experiment. Bring this practical manual along with Block 1 of BGYCT-133 course while attending the Practical Counselling session. You have read in Unit 4 Minerals of BGYCT-133 course that the physical properties of minerals are helpful in their identification. Each mineral displays some physical properties that can be recognised megascopically. Minerals show some of the important physical properties like colour, transparency, streak, lustre, hardness, specific gravity, form, fracture and cleavage. The diagnostic properties are unique properties that each mineral possess and on their basis the mineral can be easily identified. 5.3 OLIVINE Olivine is a nesosilicate mineral. The physical properties of olivine are given in Table 5.1. Now try to identify the physical properties of olivine with the help of photograph of hand specimen given in Fig. 5.1. 80 ……………………………………………………..………………………………………………………………Experiment 5 Study of Physical Properties of Minerals-II Fig. 5.1: Granular form of olivine. Table 5.1: Physical Properties of Olivine. S.N. Physical properties Characteristics 1. Crystal system Orthorhombic 2. Colour It is olive green, but also shows yellow-green to bright green 3. Transparency Opaque Mostly granular or massive and sometimes foliated, crystals 4. Form /Habit are uncommon, 5. Streak Colourless or white grey 6. Hardness 6.5-7 7. Cleavage Absent 8. Fracture Conchoidal 9. Lustre Vitreous, dull 10. Specific gravity 3.2-4.4 11. Chemical composition (Mg Fe)2 SiO4 Colour - olive green; form - granular or massive; lustre - 12. Diagnostic properties vitreous to dull; cleavage - absent; cleavage Occurrence: Olivine is magmatic in origin and occurs in both mafic and ultramafic igneous rocks. Dunite is the monomineralic rock which is totally made of olivine mineral. It occurs in some metamorphic rocks as a primary mineral. It is uncommonly present in sedimentary rocks due to its susceptible nature to weathering. Uses: Olivine is less commonly used in industry. It is used in blast furnaces for removal of impurities from iron. It is often used in metallurgical processes as a 81 …………………………………BGYCL-134 ….…………………………………………………………………………………Crystallography, Mineralogy and Economic Geology:Laboratory slag conditioner. The minerals peridot and chrysolite are the precious transparent varieties of olivine which are used as gemstones. 5.4 AUGITE Augite is a single chain inosilicate structure. It is commonly a rock forming mineral and crystallises in monoclinic system. The physical properties of augite are given in Table 5.2 and Fig. 5.2. Occurrence: Augite is a common rock forming mineral mostly found in mafic and ultramafic igneous rocks like basalt, gabbro, peridotite, etc. It is also found in diorite, granodiorite and andesite. Iron-rich composition can appear even in syenite and alkali granite. It is present in metamorphic rocks like amphibolite, hornblende gneiss, granulite. Due to its susceptibility to weathering, it is uncommonly found in sedimentary rocks. Uses: Augite is one of the few minerals which have less economic importance. But ‘Shajar’ a transparent variety of augite is used as gemstone. 82 ……………………………………………………..………………………………………………………………Experiment 5 Study of Physical Properties of Minerals-II Table 5.2: Physical Properties of Augite. S.N. Physical properties Characteristics 1. Crystal system Monoclinic Dark or dull green color, green, greyish-green, greenish 2. Colour brown, dark brown, black 3. Transparency Opaque Occurs as prismatic crystals and stubby crystals are also 4. Form /Habit common; the other forms are columnar, granular, massive, lamellar, fibrous 5. Streak White to light green 6. Hardness 5-6 Two set of perfect prismatic cleavage (cleavage angle 7. Cleavage 87º and 93º) 8. Fracture Uneven to splintery 9. Lustre Vitreous 10. Specific gravity 3.2-3.3 Chemical (Ca, Na) (Mg, Fe, Al) (Si, Al) O 11. 2 6 composition Diagnostic Colour – dark green, black; form – prismatic; cleavage - two 12. properties directions of cleavage with angle 87º and 93º Fig. 5.2: Dark green coloured augite mineral showing prismatic form. Notice one set distinct cleavage and second set indistinct cleavage. 5.5 HYPERSTHENE Hypersthene mineral like augite is a common rock- forming mineral. It is an inosilcate that is classified under pyroxene group of minerals. It crystallizes in orthorhombic system and forms an important iron rich orthopyroxene. Hypersthene is an intermediate member of solid solution series with two end members - enstatite and ferrosilite. A special property shown by hypersthene is the display of colour in natural light known as schillerisation. The physical properties of hypersthene are given in Table 5.3 and Fig. 5.3. Table 5.3: Physical Properties of Hypersthene. S.N. Physical properties Characteristics 1. Crystal system Orthorhombic 2. Colour Brown, grey, green, yellow-brown, greenish-brown, black 83 BGYCL-134 Crystallography, Mineralogy and Economic Geology:Laboratory ………………………………… ….………………………………………………………………………………… 3. Transparency Opaque 4. Form /Habit Occurs as prismatic stubby crystals and aggregates of rectangular crystals (Fig. 5.3) 5. Streak Light brown to greyish-white 6. Hardness 5-6 7. Cleavage Two set of perfect prismatic cleavage (cleavage angle 87º and 93º), parting is common 8. Fracture Uneven, brittle 9. Lustre Waxy, submetallic 10. Specific gravity 3.2-3.3 11. Chemical composition (MgFe)SiO3 12. Special property Schillerisation 13. Diagnostic properties Colour - dark brown; Form - prismatic stubby crystal; lustre - waxy or submetallic; cleavage - two sets with cleavage angle 87º and 93º, Fig. 5.3: Hypersthene showing brown colour, stubby prismatic crystals and waxy lustre. Occurrence: Hypersthene forms a constituent mineral of plutonic and volcanic igneous rocks. It is also found in metamorphosed igneous rocks and in stony meteorites. Uses: Hypersthene is used as a gemstone. 5.6 HORNBLENDE Hornblende belongs to amphibole group and it has a double chain inosilcate structure. Hornblende is a complex mixture of basic silicates of sodium, calcium, magnesium, and aluminum and is given by a general formula as show below: (Ca,Na)2–3(Mg,Fe,Al)5(Al,Si)8O22(OH,F)2 84 ……………………………………………………..………………………………………………………………Experiment 5 Study of Physical Properties of Minerals-II The physical properties of hornblende are given in Table 5.4 and Fig. 5.4. Table 5.4: Physical properties of hornblende. S.N. Physical properties Characteristics 1. Crystal system Monoclinic 2. Colour Black, dark green, dark brown, dark grey (Fig. 5.4a) 3. Transparency Opaque 4. Form /Habit Mostly ccurs as prismatic or tabular crystals with a diamond-shaped cross-section; also as dense groups of platy or grainy crystals; occasionally as columnar, radiating, acicular, fibrous and massive; individual crystals are rare 5. Streak Grey or pale green 6. Hardness 5-6 7. Cleavage Two sets of prismatic cleavage (cleavage angle 124º and 56º) see Fig. 5.4 8. Fracture Uneven, splintery 9. Lustre Vitreous 10. Specific gravity 2.9-3.4 11. Chemical (Ca Na)2-3 (Mg Fe Al)5 Si6 (Si Al)2 O22 (OH)2 composition 12. Diagnostic Colour - dark green, dark brown; form – prismatic, crystal properties aggregates; cleavage – 2 set with cleavage angle124º and 56º (Fig. 5.4b) (a) (b) Fig. 6.4: a) Hornblende showing prismatic form and vitreous lustre;
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