MOH OR SYSTEMS CRYSTAL CRYSTAL STRUCTURE The crystals are described by the crystal systems.
You can see the analysis by considering a crystal cube. There
7 crystal systems and each has its own elements of symmetry.
crystal systems are described by:
- Its crystallographic axes.
- The angles respectively two of the crystallographic axes around.
- The lengths of the crystallographic axes.
1. It looks set Obviously, all sides are perpendicular.
2. There are three planes of symmetry, which are perpendicular to each other and which are called 'axial planes of symmetry. " Each face on one side of this plane of symmetry is also reflected elsewhere. Or take two opposite faces of the cube between thumb and forefinger so including an axis of symmetry and rotate the cube to find a quaternary axis of symmetry. This means that for a full rotation of 360 ° one side is repeated four times.
Another axis of symmetry between opposite corners of the cube is a ternary axis of symmetry. Of them there are four in the bucket. A symmetry axis perpendicular to a pair of opposite edges is a fold axis of symmetry, of which there are six in the bucket.
3. The essence of symmetry is this: you can make a geometric operation so that one side is repeated in a different position. This means that when you operate as a rotation geometric p. eg. a new face will occupy the same position was occupied by other side before the rotation and the result can not distinguish between the rotation and look after the original appearance.
symmetry of a cube according to Phillips & Phillips (1986):
Area: A group of faces that intersect to form parallel edges, are said to constitute a zone. Zone axis: The direction of the lines of intersection between the faces of a zone, called zone axis.
1. The cube shows three sets of parallel edges, therefore consists of three zones. The three axes are orthogonal zone. The six faces of the cube are identical, each is parallel to two axes perpendicular to the third zone and zone axis. Consequently, the cube is a six-sided shape that completely enclose a space .. Therefore, a cubic form designated as a simple way.
2. When the same cube face observed in four different positions during the rotation axis is parallel to the edges cuarternario a symmetry axis, which is named cuarternario axis. In the cube cuarternarios three axes.
3. Since the cube faces have the same orientation in three positions during a complete rotation, the axis through the corners of a perfectly symmetrical cube can be described as a ternary symmetry axis or a ternary axis. Because ternary axes joining opposite corners of the cube must be four ternary axes. 4.When
turns on an axis perpendicular to a pair of opposite edges of the cube and the image is repeated twice, the axis of symmetry is called binary and binary axis. Since there are six pairs of opposite edges in the cube it must be six-fold axes
1. System cubic There are three crystallographic axes at 90 degrees apart:
alpha = beta = range = 90 °
The lengths of the axes are the same:
a = b = c
Typical forms of crystal system and symmetry elements :
The cube (eg halite, fluorite), the dodecahedron (eg garnet) and octahedron are forms of 3-axis symmetry quaternary, ternary axis of symmetry 4 and 6-fold axes of symmetry.
The tetrahedron is a 4-axis 3-axis ternary and binary.
Minerals belonging to the cubic system are:
Halite NaCl, Pyrite FeS 2 , Galena PbS, which are among other cubes. Diamond
of octahedral form, Magnetite Fe 3 O 4 formed between other octahedra. Garnet
, p. eg. Almandine Fe3Al2 [SiO2] 4 dodecahedral form, so icositetraédrica or combinations icositetraédrica and dodecahedral forms. - The dodecahedron is a simple form composed of 12 rhombic faces outline. The icositetraedro is a composite of 24 faces trapezoidal contour. Sphalerite ZnS
tetrahedral form.
2. Tetragonal system
There are 3 crystallographic axes at 90 degrees apart:
alpha = beta = range = 90 °
The parameters of the horizontal axes are the same, but are not equal to the vertical axis parameter: a = b ≠
[ is uneven ] c
Typical forms and their elements of symmetry are:
Zircon (ZrSiO 2) belongs to the tetragonal system and is p. eg. prisms pyramids bounded by top and bottom.
Cassiterite SnO 2
3. hexagonal system
There are 4 crystallographic axes, three to 120 ° in the horizontal plane and one vertical and perpendicular to them:
Y1 = Y2 = Y3 = 90 ° - angle between the horizontal axis and vertical axis.
X1 = X2 = X3 = 120 ° - angle between the horizontal axis.
a1 = a2 = a3 ≠ c with a1, a2, a3 = c = horizontal axis vertical axis. Apatite
Na5 [(F, OH, Cl) / (PO4) 3] and graphite C belong to the hexagonal system.
typical forms are the hexagonal prism and hexagonal trapezohedron sexternario axis and 6-fold axes.
4. Trigonal system
There are three crystallographic axes being equal, the angles X1, X2 and X3 each differ at 90 °:
X1 = X2 = X3 = 90 °
a1 = a2 = a3
Calcite CaCO3 and Dolomite CaMg (CO 3 ) 2 belong to the trigonal system and are often rhombohedrons.
Another way is a combination of pinacoid trigonal pyramid with 3-fold axes of symmetry.
5. Orthorhombic system
There are three crystallographic axes at 90 degrees apart:
alpha = beta = range = 90 °
parameters varied:
a ≠ b ≠ c [a is uneven uneven b c]
Example: Olivine (Mg, Fe) 2 (SiO4)
A typical form is a parallelogram and pinacoid combination with 3-fold axes of symmetry.
6. Monoclinic
There are three crystallographic axes, of which two (one of the two is always the vertical axis = axis c) are 90 degrees apart:
range alpha = beta = 90 ° and is greater than 90 °
parameters are unequal.
a ≠ b ≠ c [a is uneven b is uneven c]
Example: Mica
7.Sistems triclinic
There are three crystallographic axes, none of them at 90 degrees apart:
alpha beta uneven uneven uneven range of 90 °
parameters are unequal.
a ≠ b ≠ c [a is uneven b is uneven c]
Example: Albite: NaAlSi 3 8 0 and kyanite: SiO 2 Al 5
