Lecture 13

Namaskar. So, in the last lecture, we saw that how minerals are made due to magma, but we will talk about it in more depth. And this was the last slide, where we left the mode of formation of minerals. It is made in three ways. One is cooling of magma, second is weathering process, and third is metamorphic process. So, these locations we have already discussed that where all there is magma source. And if we look at the earth, how magma and after coming up, how the lava flow looks like. Now, if we look at the important rock forming minerals, then more than 70 percent of the earth's crust is made up of oxygen and silicon. In order of abundance, followed by oxides, carbonate, phosphates and sulphates. So, silicate minerals are minerals which comprises silicate, tetrahedron, silicate ions. And examples of this are feldspar, pyroxene, amphibole, olivine, garnet, quartz, clay, mica. And second is non-silicate minerals. So, we divide it into two parts, silicate and non-silicate. Non-silicate minerals have hematite, which are oxides, sulphates, galena, chalcopyrite and carbonates, in which example of calcite is given. Sulphates are gypsum and phosphates are apatite minerals. So, these two parts are divided into silicate and non-silicate minerals. So, in non-silicate and silicate minerals, first we look at silicate minerals. So, feldspar is a very good example and it is found in a large quantity. So, this is also a feldspar. So, this is a feldspar. So, this is a feldspar. So, this is a feldspar. So, this is a feldspar. So, this is a feldspar. So, this is a feldspar. So, this is a feldspar. So, this is a feldspar. So, this is a feldspar. So, this is a feldspar. So, this is a feldspar. Which is a reflection of their respective internal atomic arrangement. or orthorhombic, hexagonal, so we will see that now. This geometrical arrangement of atom results in different shapes of crystals, cubic example is done, prism is done, hexagonal is done, tetragonal is done, but overall it is seen that whatever minerals are made, if it is distributed on the basis of crystal forms, so this we can subdivide further into 6 systems, and these 6 systems are cubic, and in this axis, which I was saying earlier that geometry plays a very important role, so its internal axis, which we call alpha, beta, gamma, all these are made at 90 degrees, so this is a cubic system, so we call cubic as a cube, so it has a static form and all its faces are of the same length, so tetragonal is when, in which the axis is alpha, beta, gamma, all this is of the same length, but this is, sorry, it has the same angle, but the length varies here, although it is the same in cubic, so it is tetragonal, in hexagonal it is tetragonal, in hexagonal it is tetragonal, in tetragonal it is tetragonal, in tetragonal it is tetragonal, in tetragonal it is tetragonal, in tetragonal it is tetragonal, in tetragonal it is tetragonal, in tetragonal it is tetragonal, in tetragonal it is tetragonal. So, this is the tetragonal axis.