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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

5.1 INTRODUCTION

In the previous Experiment 4, you have identified the 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 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, 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, , 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. 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, 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 .

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, . 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 .

82 ……………………………………………………..………………………………………………………………Experiment 5 Study of Physical Properties of Minerals-II Table 5.2: Physical Properties of Augite. S.N. Physical properties Characteristics 1. 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 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 - 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 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; and b) Two set cleavage at 124o-56o. Occurrence: Hornblende is a commonly occurring rock-forming mineral of igneous rocks (granite, syenite, diorite, gabbro, basalt, andesite) and metamorphic rocks (gneiss, schist). Hornblendite is a dark coloured rock typically formed with major constituent of hornblende mineral. Uses: Hornblende is a rarely used mineral. It is used in knowing the depth of formation of plutonic rocks and as well as in mineral exploration. 85 …………………………………BGYCL-134 ….…………………………………………………………………………………Crystallography, Mineralogy and Economic Geology:Laboratory 5.7 GARNET

Garnet minerals have a nesosilicate structure with divalent and trivalent cations. They are equidimensional minerals and have the ability to occur as

independent crystals. The general formula of garnet minerals being X3Y2Si3O12 , 2+ where X = divalent ions such as Ca , Mg, Fe, Mn etc., and Y = trivalent ions such as Al3+,Fe,Cr , Ti etc. You have read about the principal minerals of garnet group in BGYCT-133 course. The physical properties of garnet are given in Table 5.5. You can see rhombohedral form of garnet in Fig. 5.5a.

(a)

(b) Fig. 5.5: a) Rhomboherdal form of garnet.; and b) Reddish brown colour natural garnet with its faceted counterparts from Bastar, Chhattisgarh. (Photo credit: Dr. Sandeep Vansutre) Occurrence: Garnet is a typical mineral found in metamorphic rocks and in few igneous rocks, particularly granites and granitic pegmatites formed under conditions of high temperature and pressure. The mineral almandine is commonly present in metamorphic rocks and minerals such as pyrope and uvarovite are generally found in ultrabasic rocks like kimberlite and peridotite. Garnet is present in clastic sedimentary rocks as heavy fraction. Uses: Garnet is used as a gemstone. Due to its hardness, absence of cleavage and affinity to break into uneven grains makes the mineral more suitable for using it as an abrasive.

86 ……………………………………………………..………………………………………………………………Experiment 5 Study of Physical Properties of Minerals-II Table 5.5: Physical Properties of Garnet. S.N. Physical properties Characteristics 1. Crystal system Isometric Commonly red or reddish brown, orange pink 2. Colour colour, pale brown, pale green colour 3. Transparency Transparent to opaque Crystals (rhombododecahedron form) 4. Form /Habit common, also occurs as granular, massive 5. Streak White or grey 6. Hardness 6.5-7.5 7. Cleavage Absent 8. Fracture Conchoidal to uneven 9. Lustre Vitreous to resinous 10. Specific gravity 3.5-4.3

11. Chemical composition Fe3Al2(SiO4)3 (almandine) Colour - reddish brown colour; form - 12. Diagnostic properties rhombododecahedron, massive; hardness - 6.5-7.5; cleavage - absent

5.8 Kyanite

Kyanite is a aluminum silicate group mineral and has a nesosilicate structure. The physical properties of kyanite are given in Table 5.6. You can observe the bladed form and typical blue colour in kyanite in Fig. 5.6.

Fig. 5.6: Note inky bluish grey colour and bladed form of kyanite. Occurrence: Kyanite mainly occurs in metamorphic rocks such as schists and gneisses. It is also found in sedimentary rocks as detrital grains in heavy mineral fraction. Uses: Mineral kyanite is used in the manufacture of grinding wheels and cutting wheels due to its hardness. It is also used in the manufacture of ample variety of products such as abrasives, insulators, ceramics and refractories. It is used as an index mineral to know the different conditions like pressure, temperature and depth under which the rock as undergone metamorphism. Some of its varieties are used as gemstones. 87 …………………………………BGYCL-134 ….…………………………………………………………………………………Crystallography, Mineralogy and Economic Geology:Laboratory Table 5.6: Physical Properties of Kyanite. S.N. Physical properties Characteristics 1. Crystal System Triclinic Normally light to dark blue, indigo-blue, shades 2. Colour of blue; rarely colourless, white, grey, green, orange, or black 3. Transparency Transparent to translucent Generally occurs as long and slender bladed 4. Form /Habit crystals. Also occurs as radiating, reticulated and flattened tabular crystals 5. Streak White, colourless It has hardness of 4.5 to 5 along the length and 6. Hardness 6.5 to 7 across the width of the crystal Perfect in two directions, exceptionally we find 7. Cleavage the faces to be striated 8. Fracture Uneven to hackly 9. Lustre Vitreous, greasy 10. Specific gravity 3.5-3.7

11. Chemical composition Al2SiO5 Colour - blue to indigo; form - bladed; hardness - variable 4.5 to 5 along the length of the crystal 12. Diagnostic properties and 6.5 to 7 across the width of the crystal ; cleavage - 2 sets; crystal faces are striated

5.9 NEPHELINE

Nepheline is a rock-forming mineral of feldspathoid group rich in potassium aluminosilicates. Nepheline is also called as ‘nephelite’ and it is mostly found in alkali rich rocks like nepheline syenite. It is a tectosilicate mineral. Massive variety of nepheline with a greasy lustre is named as ‘eleolite’. The physical properties of nepheline are given in Table 5.7 and Fig. 5.7.

Fig. 5.7: Inky blue nepheline. 88 ……………………………………………………..………………………………………………………………Experiment 5 Study of Physical Properties of Minerals-II

Table 5.7: Physical Properties of Nepheline. S.N. Physical properties Characteristics 1. Crystal System Hexagonal 2. Colour White, grey or bluish 3. Transparency Translucent to opaque Crystals uncommon, often massive or granular, 4. Form /Habit rarely prismatic to columnar crystals Colourless, white and to some extent reddish 5. Streak white 6. Hardness 5.5-6 Poor in three directions, prismatic, but rarely 7. Cleavage seen One set of cleavage is distinct 8. Fracture Subconchoidal to uneven 9. Lustre Vitreous or greasy 10. Specific gravity 2.60-2.65 Chemical Na KAl Si O 11. 3 4 4 16 composition Reactive to acids and it does not bubble like 12. Special property many of the carbonates Colour- greyish, bluish, inky blue; form- 13. Diagnostic properties coarsely crystallized; lustre-greasy

Occurrence: Generally, nepheline occurs in alkali rich and silica deficient rocks. It is found in both the plutonic and volcanic igneous rocks and in pegmatite associated with nepheline syenite. Uses: Nepheline serves as an ore of aluminium. Pure nepheline and nepheline- feldspars are used in the manufacture of ceramics and glass. It is also used in the extraction of rare alkaline metals and gallium.

5.10 CHLORITE

Chlorite group represents the sheet silicate (phyllosilicate) minerals formed during early phases of metamorphism. Clinochlore, pennantite and chamosite form the common minerals of the chlorite group. The physical properties of chlorite are given in Table 5.8 and Fig. 5.8. Occurrence : They are found in all the three types of rocks such as igneous, metamorphic and to a less extent in sedimentary rocks. They are found in the rocks formed by hydrothermal activity or contact metamorphism. Chlorite occurs in low-grade schists of metamorphic rocks. It is abundantly found as alteration product of biotite and other ferromagnesium minerals in igneous rocks. It is also found in fraction of clay rich sediments. It occurs in some sedimentary iron ores like chamosite (an iron-rich chlorite). Uses: Commercially, the mineral chlorite has less importance. It is mostly used as a crushed stone.

89 …………………………………BGYCL-134 ….…………………………………………………………………………………Crystallography, Mineralogy and Economic Geology:Laboratory

Fig. 5.8: Green colour flaky chlorite. Table 5.8: Physical Properties of Chlorite. S.N. Physical properties Characteristics 1. Crystal System Monoclinic Typically green, but some varieties show orange to 2. Colour brown, violet 3. Transparency Transparent to translucent Commonly found as scaly aggregates and as fine 4. Form /Habit grained and earthy masses 5. Streak White, pale green 6. Hardness 2.5 7. Cleavage Perfect, cleavage flakes are flexible but not elastic 8. Fracture Uneven 9. Lustre Vitreous to earthy 10. Specific gravity 2.7- 2.9

11. Chemical composition (Mg,Fe)5Al((Al,Si)3O10(OH)8 Colour: typical green colour; form- scaly aggregates; 12. Diagnostic properties cleavage-perfect cleavage and flakes are flexible but not elastic

5.11 EPIDOTE

The common minerals of the group are zoisite, clinozoisite, epidote and allanite. The physical properties of epidote are given in Table 5.9 and Fig. 5.9. Occurrence: Epidote is found as principal constituent of calcium aluminium silicates of low and medium grade metamorphic rocks. It occurs in contact- metamorphosed limestones that are found in association with iron ores. It is found commonly with zeolites associated with amygdules and other cavity structures of basalts.

90 ……………………………………………………..………………………………………………………………Experiment 5 Study of Physical Properties of Minerals-II Uses: Commercially the epidote mineral has less industrial value. It is less importantly used as a gemstone. Table 5.9: Physical Properties of Epidote. S.N. Physical properties Characteristics 1. Crystal System Monoclinic Pistachio green, yellowish to brownish green 2. Colour to black 3. Transparency Transparent to translucent 4. Form /Habit Commonly granular and massive, fibrous 5. Streak White or greyish white 6. Hardness 7 7. Cleavage Perfect 8. Fracture Uneven 9. Lustre Vitreous 10. Specific gravity 3.3-3.6 Chemical Ca (Al,Fe) (SiO4) (OH) 11. 2 3 3 composition Colour - Pistachio green, yellowish green 12. Diagnostic properties colour; form - granular form, hardness 7, perfect cleavage

Fig. 5.9: Pistachio green, massive and granular epidote.

5.12 LABORATORY EXERCISES

Study the physical properties of common rock forming minerals like olivine, augite, hypersthene, hornblende, garnet, kyanite, nepheline, chlorite and epidote by following the instructions given here:

91 …………………………………BGYCL-134 ….…………………………………………………………………………………Crystallography, Mineralogy and Economic Geology:Laboratory 1. Get hand lens, pen knife, streak plate, coin, hardness box, broken glass piece and mineral specimen from your academic counsellor. 2. Study the physical properties of the mineral by taking mineral specimen in hand and observe its properties with the help of the devices provided by your academic counsellor. 3. Write down all the properties of the mineral specimen that you have observed in the laboratory file and infer its diagnostic /special properties from the physical properties that you have examined. 4. From the physical properties and especially the diagnostic/special properties you have observed and known, identify the mineral name and write it on the laboratory file. 5. Finally, write down the mineral occurrences and uses from the knowledge you have gained while studying the theory and practical courses. 6. If you find any problem during the study of the mineral specimens do not hesitate to ask your counsellor. 7. Handle the mineral specimens and all the devices provide to you with great care and do not damage them. Exercise 1: Identify the given mineral specimen by studying its physical properties and write them in your laboratory file. Study all the minerals one by one as identified above and write the physical properties of the mineral specimens in the manner as listed below. Also mention the diagnostic physical properties used by you for the identification of that particular mineral.

S.N. Physical properties Characteristics

1. Crystal system

2. Colour

3. Transparency

4. Form /Habit

5. Streak

6. Hardness

7. Cleavage

8. Fracture

9. Lustre

10. Specific gravity

11. Chemical composition

12. Special property

13. Diagnostic properties

92 ……………………………………………………..………………………………………………………………Experiment 5 Study of Physical Properties of Minerals-II

Exercise 2: Write the occurrence and uses of the minerals studied by you, belonging to pyroxene and amphibole groups.

Exercise 3: How would you distinguish between following pairs:  Augite and hypersthene  Augite and hornblende  Nepheline and kyanite  Chlorite and epidote  Garnet and olivine Exercise 4: Write the occurrence and uses of olivine, epidote, chlorite and olivine.

5.13 LEARNING RESOURCES

 Microscopic Study of Basaltic Rocks Link: https://www.youtube.com/watch?v=2RGL3XB2x3E&t=2s  Identifying the Rock forming minerals Link: https://www.youtube.com/watch?v=n5p0hHZT2gg  Specific Gravity | Physical Properties of Minerals Link: https://www.youtube.com/watch?v=o0WGcvG1YBk

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