IIT JAM

follow

Top Resources

G

Gurmeet Singh posted an Question

November 04, 2020 • 04:58 am

30 points

IIT JAM
Geology (GG)

Is there any way to learn this concept?. please suggest

. Class 'm3m' belong to: A. Trigonal system B. Isometric system C. Hexagonal system D. Triclinic system

2 Answer(s)

1 Likes
4 Comments
0 Shares

>
Saurabh 1

Answer will be (B) Isometric system. m3m is a centrosymmetric class of cubic system (including m3, if the point group is like m 3bar m then it is equivalent to hexoctahedral class (4/m 3 bar 2/m). And it cannot be trigonal or hexagonal cuz this crystal class is not compatible with the hermann mauguin symbol of both the crystal systems( for any arbitrary or point group abc, you will never find in trigonal and hexagonal system that b is 3, which is the case with isometric only)... If you are a beginner you can learn these concepts from Cornelis klein, which is a slightly advanced book but a good book for concept regarding crystallography or you can go through the standard book like Dexter Perkins, which is more than enough for any competitive exams (jam, gate, university entrance exams)... Thanks...
- Likes(0)
- Reply(2)
what is m here
- Like(0)
m stands for mirror plane or you can say each unique mirror plane present in the crystal class... just like for orthorhombic if the crystal class is 2mm then it means it has one two fold axis and two mirror plane(m is choosen in the way it is unique in the sense independent of the other mirror plane if exist).
- Like(0)

>
Sajan sarthak

gurmeet please mark all the answers by me before leaving take care and keep growing
- Likes(1)
- Reply(0)

>
Sajan sarthak

The second symbol is a 3 fold axis so you can guess it as Isometric system which contains 4 axis of 3 fold symmetry. i.e the characteristics of isometric system. But m3m HM symbol is not in the 32 point group.
- Likes(0)
- Reply(0)

>
Rahul kumar Best Answer

Answer (B) Isometric system Yes, there is a concept behind identifying the point groups. Any point group is expressed in form of "abc". If b= 3 or bar3 then the point group will belong to isometric system. For example; abc = m3m; Here, b= 3 so, m3m must belong to isometric system.
- Likes(1)
- Reply(5)
what if solution is trigonal , hexagonal
- Like(1)
Considering idealized symbol of point group in form of "abc" For trigonal a= 3 or bar3. For hexagonal, a=6 or bar6. For tetragonal a= 4 or bar4 and b is not equal to 3.
- Like(1)
where i should read this sir
- Like(1)
From Perkins book
- Like(1)
You can read this concept in Dexter Perkins Mineralogy book.
- Like(1)

T