Mineralogy Lab exam

Geometry of packing in planar patterns.

Oblique, square, hexagonal

Four rotational symmetry elements

Mirror plane (reflection), fold axes (rotation), center of symmetry (i), rotoinversion (rotation + inversion)

Writing H-M symbols

1. Determine overall symmetry content of the crystal

2. list each symmetry element present

3. determine total of each element present

4. determine different # of kinds present ** most important 

H-M rotation axes

Write in descending order using numbers only. Such as 4 2. list for how many times there are types. if there are 3 types of 2 fold axes 2 must be written 3 times (2 2 2) 

H-M mirror planes

If a mirror plane is perpendicular to a fold axis, the m is placed under the rotation axis, as in a fraction. m is listed as many times as there are types. 4/m 2/m 2/m .

If mirror planes are not perpendicular to rotation axes, add the m to the end of the symbol such as 4m.

H-M center of symmetry

An overbar is added to the odd-fold axes to represent presence of center of symmetry. All even fold axes have perpendicular mirror planes so it is unnecessary to state i.

if there is no center of symmetry then its H-M symbol is 1.

Miller indicies 

isometric form - textrahexahedron - 24 

Wavelength and color on a graph

The lowest point is the color that is being transmitted and the highest point is peak absorption

Isometric crystal system

a1,a2,a3 - perpendicular mirror plane 2 kinds (9 total 2 kinds)

4/m 3 bar, 2/m

Tetragonal Crystal system

A4= C A2= A1, A2 

3 types of mirror planes all perpendicular to fold axes. 

4/m 2/m 2/m 

Orthorhombic

a,b,c all perpendicular to 3 types of mirror planes. A2= a,b,c

2/m 2/m 2/m

Hexagonal crystal system

C, a1, a2, a3. 3 types of mirror planes all perpendicular to axes. A6(orA3)=C

A2= 2 axes

6/m, 2/m, 2/m

Other type- hexagonal rhombohedral - the 3 fold

Monoclinic crystal system

a not equal b not equal c

𝛼=Ɣ=90 β ≄ 90

A2=b 

2/m

Triclinic

a,b,c all not equal no angles equal. only center of symmetry.

Bar 1

the geologist can find amazing ores quickly through correct data

Mohs Hardness scale

Hardness of a glass plate 

H= 5.5