JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II MINING GEOLOGY Previous Question Paper (March - 2021 - R16)

The Feldspar group constitutes the most abundant mineral group in the Earth's crust. They are tectosilicates, characterized by a three-dimensional framework of linked (SiO4)4- and (AlO4)5- tetrahedra. The structure incorporates cations such as K+, Na+, and Ca2+ within the interstices of this framework.

Mineral composition is categorized into two main series: Potassium Feldspars (e.g., Orthoclase, Microcline, Sanidine with formula KAlSi3O8) and Plagioclase Feldspars (a solid solution series between Albite NaAlSi3O8 and Anorthite CaAl2Si2O8).

Physical properties include a hardness of 6 on the Mohs scale, two directions of cleavage meeting at or near 90 degrees, and a vitreous to pearly luster. Their specific gravity typically ranges from 2.55 to 2.76. Chemically, they are aluminosilicates of potassium, sodium, and calcium. They are susceptible to chemical weathering, where they alter into clay minerals like kaolinite through hydrolysis.

Rocks are broadly classified into three main types based on their mode of formation:

1. Igneous Rocks: Formed by the cooling and solidification of molten rock material (magma or lava). They are classified as intrusive (plutonic) if cooled slowly beneath the surface (e.g., Granite) or extrusive (volcanic) if cooled rapidly on the surface (e.g., Basalt).
2. Sedimentary Rocks: Formed by the accumulation, compaction, and cementation of sediments derived from pre-existing rocks or through chemical precipitation. They are classified as clastic (e.g., Sandstone, Shale), chemical (e.g., Limestone, Gypsum), or organic (e.g., Coal).
3. Metamorphic Rocks: Formed by the transformation of pre-existing rocks due to high temperature, pressure, or chemically active fluids without melting. They are classified based on texture as foliated (e.g., Gneiss, Schist) or non-foliated (e.g., Marble, Quartzite).