The crystallographic axes are the imaginary lines that we can draw within the crystal lattice. These crystal axis than works as the coordinate system within the crystal. These are well defined lines for the crystals. “On the basis of number of crystal axes and mutual relationship between them we define a crystal system“ Crystal system […]
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There are three elements of crystal forms. The face, edge and solid angle. Forms – It is a group of faces which have a like positions with respect to the crystallographic orientations. Forms may be classified in the following three ways – 1st way 2nd way 3rd way Simple form – when a crystal is
In the upper crust the pressure is less and brittle shear zone prevails whereas in the lower part pressure is enough to go for ductile shearing. Development of Textures
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The shear zones is a region in the Earth’s crust where rocks are highly strained than the surroundings. These highly strained rocks can be found in the highly structural deformed terrains. These highly strained rocks can be cohesive or they can loose cohesion. These high strained rocks are classified on the basis of Cohesion, Foliation
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In metamorphic petrology the reactions generally involves the replacement of minerals by their polymorphs and often the reactions may not complete. In many reactions, a pseudomorph may develop in which the new mineral retain the older minerals shape. “Some reactions produce intimate, typically wormy-looking intergrowths of two or more minerals called symplectite texture. Pseudomorphs may
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The carbonate mineral group form in the environment where water and carbon-di-oxide are present. The (CO3)– complex are basic building units of all carbonate minerals and are responsible for the properties to group. An acid test is widely used for identification of carbonates. Calcite Group (Hexagonal) Dolomite Group (Hexagonal) Aragonite Group (Orthorhombic) Calcite [CaCO3]Magnesite [MgCO3]Siderite
Garnets is a group of 6 members that are crystallizes in the cubic system with a profound rhobdodecahedral cleavage. Structure Physical and Optical Properties Physical propoerties Optical properties Varities – There are many varities of the Garnet minerals – Occurance –
The mica group of minerals crystallizes in the monoclinic system. They are phyllosilicates with their general formula as – X2Y4-6Z8O20[OH,F]4 Where, X = K, Na, Ba, Ca Y = Al, Mg, Fe+2, Li, Cr, Mn, Zn Z = Si, Al, Fe+3 STRUCTURE physical and optical properties physical properties optical properties Mode of occurrence –
Beta diagrams are generally preferred for analysis of faults, ore shoots, kink-bands and rotational manipulations but for complexly folded terrains, Pi diagrams are preferred. Beta diagram beta diagram A stereographic diagram which represents the trend and plunge of the line produced by the intersection of two planes. In its application in structural geology, the dip and strike of a fold surface / lineation/ bedding are recorded as a great circle,
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Pyroxenes are formed either direct or by the reaction of olivine with quartz. Structure Important minerals – Optical Properties Orthopyroxene Clinopyroxene Alteration – Orthopyroxene alter to serpentine or fibrous amphibole. Augite alters to chlorite/ hornblende. Varities – Occurances – REFERENCES –
