UNIT-II MINERALOGY

1. UNIT-IIMINERALOGY

2. MINERALOGY • A mineral is naturally occurring homogeneous inorganic substance having distinctive physical properties and a more or less definite chemical composition. • Minerals are to a large extent the units which make up the rocks of the earths crust or the outer shell.

3. MODE OF FORMATION OF MINERALS • Three kinds of formation of minerals in nature • Formed from magma • Secondary process • Metamorphism • Directly formed from deposition of molten magma - feldspar, quartz, pyroxenes, amphiboles, micas • Due to weathering, precipitation, deposition (secondary process) – calcite, dolomite, bauxite, coal, petroleum • Formed under the influence of high temperatures and pressures with and without the active involvement of chemically active solution (metamorphism)- Garnets, chlorite, graphite

4. CRYSTALLOGRAPHY • Great majority of minerals when the conditions of formations are favorable, occur in definite and characteristic geometric forms known as crystals. • Crystal-Greek word “Krystallos” meaning clear ice. • The study of crystals is called as crystallography.. • “Crystals are bodies bounded by surfaces usually flat, arranged on a definite plan which is an expression of an orderly internal arrangement of the atoms”.

5. CRYSTALLOGRAPHICARRANGEMENT

6. SYMMETRY • All crystals show by the arrangement of their faces a definite symmetry which enables one to group them into different classes • Types of symmetry • Plane of symmetry • Axis of symmetry • Centre of symmetry

7. SYMMETRY 1.PLANE OF SYMMETRY A plane of symmetry divides a crystal into two similar and similarly placed halves 2.Axis of symmetry If a crystal on being rotated comes to occupy the same position in space more than once in a complete turn the axis about which the rotation has taken Is called as axis of symmetry 3.Centre of symmetry A crystal is said to have centre of symmetry if an imaginary line can be passed from any point on its surface through its centre and a similar point can be found on the line at an equal distance beyond the centre

8. PHYSICAL PROPERTIES • Colour • Lustre • Structure • Hardness • Cleavage • Fracture • Specific gravity • Tenacity • Odour and taste

9. Colour very useful in identifying mineral in spite of the fact that colour is constant in most of the minerals and commonly colour is due to stain or impurities in the minerals. Lustre Appearance of a fresh surface of a mineral in a ordinary reflected light Metallic- galena Glassy-vitreous Pearly-talc Structure Term used to denote the shape and form of minerals. • Columnar • Bladed • Fibrous • Radiated • Lamellar • granular

10. Hardness Resistance a mineral offers to abrasion or scratching and is measure relative to a standard scale of ten minerals known as Moh’s scale of hardness Cleavage Tendency of many crystallized minerals to break or split in certain parallel directions yielding more or less smooth surfaces known as cleavage planes. May be perfect and imperfect Fracture Appearance of the broken surface of the mineral. Specific gravity Specific gravity of a mineral is the ratio of its weight to the weight of an equal volume of water.

11. Tenacity The resistance which the mineral offers to breaking, crushing, bending or tearing-in short its cohesiveness is known as tenacity Ex Brittle, sec tile, malleable, flexible and ductile Taste A few minerals which are soluble in water have more or less characteristic tastes Acid, alkaline, astringent, bitter, cooling, pungent, saline

12. ISOMORPHISM • Peculiar natural phenomenon • Minerals appear to be mixtures of two different minerals from chemical composition. • This type of formation is called as isomorphism • Examples: Feldspar, pyroxene, amphiboles and garnets

13. ROCK FORMING MINERALS • Silicate ranks first in the earths crust for rock forming minerals. • SiO4 tetrahedron ins the fundamental unit of all silicate minerals. STRUCTURE OF SILICATES: • Nesosilicates - SiO4 occurs as Independent unit E.g. garnet. • Sorosilicate - SiO4occurs as pairs unit E.g. garnet. • Inosilicate - SiO4occurs as chains along one direction or single chain silicates e.g. pyroxenes • Cyclosilicates - SiO4occurs as ring form as 3 or 4 units called as ring silicatese.g beryl • Phyllosilicates - SiO4occurs as sheets; called as sheet silicates. E.g mica, chlorite • Tectosilicates - SiO4occurs as three dimensional frame work e.g quartz, feldspar

14. MINERAL GROUP OR FAMILIES • Some silicate minerals have similar atomic structure and chemical composition. Such set of minerals are called as groups or families. Examples of some important groups of silicate minerals • Feldspar group • Pyroxene group • Amphibole group • Garnet group

15. IMPORTANT DETAILS OF ROCK FORMING MINERAL I. FELDSPARS • Most abundant of all the silicate minerals. • The name refers to a group and not a single mineral • Make up about half the rocks of earths crust • Form monoclinic and triclinic crystals and are aluminous silicates of K, Na or Ca. • Three common molecules • Orthoclase - KAlSi3O3 • Albite - NaAlSi308 • Anorthite - CaAlSi3O8

16. CRYSTAL SYSTEM : MONOCLINIC Any mineral that falls under the following specifications belongs to the monoclinic crystal system. • Threeaxes, all of them are unequal in length. Two of them are at right angles to each other, while the third is lies at an angle other than 90°.

17. CHEMICAL COMPOSITION-FELDSPAR In chemical constitution, felspars are chiefly Alumino-silicates of sodium, potassium and calcium with the following general formula : WZ4O8 whereW=Na ,K, Ca and Ba and Z= Si and Al . The Si : Al shows a variation of 3:1 to 1:1 . Some examples of chemical composition of felspar minerals are : KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8 Occurs in isomorphous series

18. ATOMIC STRUCTURE-FELDSPAR At atomic level ,the felspars shows a continuous three-dimensional network type of structure in which SiO4 tetrahedra are linked at all the corners, each oxygen ion being shared by two adjacent tetrahedral. The SiO4 tetrahedra is accompanied by AlO4 tetrahedra so that the feldspar are complex three dimensional framework of the above two types of tetrahedra. The resulting network is negatively charged and these negative charges are satisfied by the presence of positively charged K, Na, Ca and Ba. The felspar group of minerals crystallize only in two crystallographic systems Monoclinic and Triclinic.

19. CRYSTALLIZATION The feldsdpargroup of minerals crystallize only in two crystallographic systems Monoclinic and Triclinic. CLASSIFICATION Chemically felspar fall into two main groups: • The potash felspar • The soda lime felspar . Common members of the two groups are - Potash felspar : Orthoclase (KAlSi3O8), Sanidine(KAlSi3O8) and Microline (KAlSi3O8). Soda – lime feldspar : These are also called the plagioclase feldspars and consists of an isomorphous series of six felspar with two components: NAlSi3O8 and Ca Al2 Si2O8 as the end members. 1. Albite 4. Labradorite 2. Oligoclase 5. Bytwonite 3. Andesine 6. Anorthite The above series is also known as Albite-Anorthite series.

20. Crystallographically,felspar fall in two crystal systems . Monoclinic Feldspars 1. Orthoclase (KAlSi3O8 ) 2. Sanidine (KAlSi3O8 ) Triclinic Feldspars 1. Microcline (KAlSi3O8 ) • 2. Albite– Anorthiteseries (six minerals)-(six minerals) PHYSICAL PROPERTIES • In addition to their close relationship in chemical composition ,crystallography and atomic constitution ,felspar group of minerals exhibit a broad similarity and closeness in their physical characters as well so that differentiation of one variety from other requires very thorough, sometimes microscopic examination. • Light in colour, • lower specific gravity , • have a double cleavage and a hardness varying between 6-6.5. • COMMON TYPE OF MINERALS • Orthoclase 2. Microcline 3. Albite 4. Anorthite

21. PHYSICAL PROPERTIES-FELDSPAR

22. Orthoclase

23. microcline

24. albite

25. anorthite

26. II. QUARTZ • Composition of SiO2 • Most abundant material next to felspar • Colourless or white • Many coloured varieties are mainly due to impurities. • Three main varieties • Crystalline -Rock crystal, amethyst, rose quartz, milky quartz • Crypto-crystalline -Chalcedony, carnclian • Amorphous-opal Mostly used for jewellery and ornamental purposes

27. QUARTZ

28. Polymorphous transformation Quartz, when heated , transforms into high temperature modifications as follows: (870•C) (1470•C) (1713•C) Quartz ↔ Tridymite ↔ Cristobalite ↔ melt The variety named as QUARTZ itself has two polymorphs : 1. Α quartz, 2. β quartz. Identification of the exact type of quartz (into Αand β) requires thorouginvestigations of the mode of formation of mineral as observed by its place of occurrence and also type of symmetry. • Right handed and left handed quartz : • When occurring, quartz may be distinguished into right handed and left handed types. • Carried out on the basis of recognition of some typical faces such as trigonal, trapezohedron and dipyramid. These two faces normally occur at the edges of the prism faces, one above the another. In the left handed quartz ,these faces are located on the left side of the upper edge of the prism, whereas in the right handed quartz, these occur on the right upper edge of the crystals. Such a location of these faces in manifestation of an internal atomic arrangement in the crystal.

29. COLOURED VARIETIES : Common pure quartz is a colourless transparent mineral. Presence of even a trace of an impurity may give it a characteristic colour and hence a variety . A few common types of quartz distinguished on their basis are : • Amethyst – purple or violet • Smoky- dark to light brown, even black • Milky- pure white and opaque • Rose red – colour is attributed to presence of titanium.

30. CRYPTOCRYSTALLINE TYPES : In many cases, crystalline of pure silica to quartz remains incomplete due to interruption in the process for one reason to another. Silica occurring in these cryptocrystalline varieties, although close in composition and physical properties to quartz is named differently. A few common varieties of cryptocrystalline silica are as follows : • Chalcedony – luster ,waxy, commonly translucent, generally massive. • Agate – often banded , opaque and massive. • Onyx – a regularly banded agate having alternating and evenly paced layers of different colours. • Flint – a dull opaque variety of chalcedony breaking with characteristic conchoidal fracture. • Jasper- a dull red, yellow,almost amorphous variety of silica. OCCURRENCE Quartz and its varieties occur in all types of rocks ;igneous, sedimentary and metamorphic. In igneous rocks, quartz makes up bulk of acidic varieties. In sedimentary rocks quartz makes up sandstones and orthoquartzites. Loose sands consist mostly of quartz grains. The metamorphic rocks like gneisses contain good proportion of quartz in some cases. A metamorphic rock named as (Para) quartzite is entirely made up of quartz.

31. PIEZOELECTRICITY Quartz crystals have piezoelectric properties; they develop an electric potential upon the application of mechanical stress. An early use of this property of quartz crystals was in phonograph pickups. One of the most common piezoelectric uses of quartz today is as a crystal oscillator. The quartz clock is a familiar device using the mineral. The resonant frequency of a quartz crystal oscillator is changed by mechanically loading it, and this principle is used for very accurate measurements of very small mass changes in the quartz crystal microbalance and in thin-film thickness monitors. Quartz scepters

32. PHYSICAL PROPERTIES-QUARTZ

33. III. PYROXENE • Constitute important group of minerals that are generally recognized by their stout crystals and their two cleavages right angles to each other. • Most pyroxenes are dark coloured • Ca, Mg and Fe silicate composition • Varieties • Monoclinic pyroxene - Augite • Orthorhombic pyroxene - Hypersthene

34. CHEMICAL COMPOSITION • Composition mainly consists of silicates of calcium, magnesium and ferrous iron. • At initial formation magnesium rich varieties • At later stage iron rich formation • General formula R2(AlSi)2 where R –divalent calcium, magnesium or ferrous iron ATOMIC STRUCTURE • Single chain silicates • Have 1:3 ratio of silicon and oxygen • Mostly crystallize in the form of either orthorhombic or monoclinic system

35. Monoclinic pyroxene- AUGITE

36. AUGITE - description • Chemical Formula: (Ca,Na)(Mg,Fe,Al)(Al,Si)2O6 • Augite is an important rock-forming mineral, and large crystals are fairly common. • It is the most widespread member of the pyroxene group, and it frequently alters to many other minerals, including Hornblende. • Augite usually occurs in dull crystals that are ugly and uninteresting. • The name Augite is derived from the Greek word augites, "brightness", in reference to the bright luster this mineral occasionally exhibits.

37. OCCURRENCE • Major rock forming mineral in mafic igneous rocks, ultramafic rocks and some high grade metamorphic rocks.

38. Crystal System : Monoclinic • Any mineral that falls under the following specifications belongs to the monoclinic crystal system:Three axes, all of them are unequal in length. Two of them are at right angles to each other, while the third is lies at an angle other than 90°.

39. AUGITE – PHYSICAL PROPERTIES • Colour : dark green to black • Streak : white to gray, augite can be slightly harder than a streak plate so brittle fragments rather than a powder will sometimes be produced. • Lustre : vitreous • Diaphaneity : translucent to opaque • Cleavage : prismatic • Hardness : 5.5 – 6 • Specific Gravity : 3.2 - 3.6 • DistinguishingCharacteristics : Two cleavage directions almost at right angles, dark green to black colour • Chemical Classification : silicate

40. USES OF AUGITE • Augite is a dark green to black mineral that is used for ceramics. • It contains large amounts of aluminum, iron, and magnesium and can be found in meteroic stones. • ceramic glazing, manufacturing aluminum, purifying water.

41. IV.AMPHIBOLES Crystals – long, slender, prismatic, sometimes fibrousPrism angle – 124’ Another type of mineral AMPHIBOLE MINERALS Important Crystallization ORTHORHOMBIC MONOCLINIC

42. Amphibole Group – Resemble – Pyroxene Group CHARACTERISTICS • HARDNESS: 5 – 6 • SPECIFIC GRAVITY: 3 – 3.5 • Dark in Colour CHEMICAL COMPOSITION • Amphibole minerals – Metal silicates – Si : O – 4 : 11 • Ca, Mg, Fe, Mn, Na, K, H – metallic ions • (OH) ions – F and Cl – • Chemical Formula – [Si4 O11]2 [OH]2 • Various ions – Al, Mg, Fe, Ca, Na, K, H, F – replaced – giving rise to a variety of Amphibole minerals ATOMIC STRUCTURE • Difference – Amphiboles and Pyroxenes • Amphiboles – SiO4 tetrahedra – double chains • Reason – more complex than Pyroxenes – chemical composition

43. PHYSICAL PROPERTIES • Crystallise in only 2 crystal systems • Dark in colour. • Hardness – 5 to 6 • Specific Gravity – 2.8 to 3.6 • Elongated • Slender • Often fibrous in nature Orthorhombic Amphiboles ANTHOPHYLLITE (Mg, Fe)3 [Si4O11]2 [OH]2

44. VARIETIES OF AMPHIBOLES • Hornblende • Tremolite • Actinolite • Asbestos Hornblende is the most common variety

45. AMPHIBOLE - 1.Hornblende

46. Hornblende – Description • Chemical formula : Ca2(Mg,Fe)4Al(Si7Al)O22(OH,F)2 • Any of a subgroup of amphibole minerals that are calcium-iron-magnesium-rich and monoclinic in crystal structure. • Hornblende, occurs widely in metamorphic and igneous rocks. • Common hornblende is dark green to black in colour and usually found in middle-grade metamorphic rocks (formed under medium conditions of temperature and pressure). • Such metamorphic rocks with abundant hornblende are called amphibolite's.

47. System :Monoclinic • Block diagram showing the relationship between the crystallographic axes and the indicatrix axes.

48. OPTICAL PROPERTIES • Colour : distinctly coloured, shades of green, yellow-green, blue-green and brown • Composition : exhibits a wide range of compositions. • Occurrence : common mineral found in a variety of geological environments, i.e. in igneous, metamorphic and sedimentary rocks • Alteration : may be altered to biotite, chlorite or other Fe-Mg silicates • Distinguishing Features : cleavage and grain shape, inclined extinction, pleochroism

49. PHYSICAL PROPERTIES • Colour : dark green to black. • Streak : grayto greenish gray • Lustre : vitreous • Diaphaneity : translucent to nearly opaque • Cleavage : good • Hardness :5.0 - 6.0 • Specific Gravity : 3.0 - 3.5

50. USES • The hornblende mineral is used in a variety of common things that we use every day. • These things include: steel, soap, oil, buildings, and statues.