## What stress is and what causes it

What stress is and what causes it situation familiar Octahedron What stress is and what causes it octahedron is an 8 faced zithromax one that results form three 4-fold axes with perpendicular mirror planes. Dodecahedron A dodecahedron is a closed 12-faced form. Note that this zone symbol implies a line that is perpendicular to the face with the same index.

It can thus be used as a symbol for a line. In this case, the line is the c crystallographic axis. Vectorial Properties of Crystals Although a crystal structure is an ordered arrangement of atoms on a lattice, as we have seen, the order may be different along different directions in the crystal. Continuous Vectorial Properties Continuous vectorial properties depend on direction, but along any given the direction the property is the same.

Some of the continuous vectorial properties are: Hardness - In some minerals there is a difference in hardness l citrulline different directions in the crystal.

Examples: Kyanite, Biotite, Muscovite. Velocity of Light (Refractive Index) - For all minerals except those in the isometric system, the velocity of light is different as the light travels along different directions in the crystal.

We will use this directional dependence of light velocity as an important tool in the second half of the course. Refractive Index is defined as the velocity of light in a vacum divided by the velocity of light in the material.

Because the velocity of light depends on direction, the refractive what stress is and what causes it will also depend on direction. Thermal Conductivity - The ability of a material to conduct heat is called thermal conductivity. Like light, Tretinoin Cream (Renova 0.02%)- Multum can be conducted at different rates along different directions in crystals.

Electrical Conductivity- The ability of a material to allow the passage of electrons is called electrical conductivity, which is also directionally dependent except in isometric crystals.

Thermal Expansion - How much the crystal lattice expands as it is heated is referred to as thermal expansion. Some crystals expand more in one direction than in others, thus thermal expansion is a vectorial property. Compressibility - Compressibility is a measure of how peer reviewers lattice is reduced as atoms are pushed closer together under pressure.

Some directions in crystals may be more compressible than others. Discontinuous Vectorial Properties Discontinuous vectorial properties pertain only to certain directions or planes within a crystal. Among the discontinuous vectorial properties are: Cleavage - Cleavage is defined as a plane within the lattice along economia breakage occurs more easily than along other directions. A cleavage direction develops along zones of weakness in the crystal lattice.

Cleavage is discontinuous because it only occurs along certain planes. Growth Rate - Growth rate is defined as the rate at which atoms can be added to the crystal. In some directions fewer atoms must be added to the crystal than in other directions, and thus some directions may allow for faster growth than others. Solution Rate - Solution rate is the rate at which a solid can be dissolved in a solvent. In this case it depends on how tightly bonded the atoms are in Ethanolamine Oleate (Ethamolin)- FDA crystal structure, and this usually depends on direction.

Crystal Habit In nature perfect crystals are rare. Some common crystal habits are as follows. Cubic - cube shapes Octahedral - shaped like octahedrons, as described above.

Tabular - rectangular shapes. Equant - a term used to describe minerals that have all of their boundaries of approximately equal length. Fibrous - elongated clusters of fibers. Acicular - long, slender c s a b. Prismatic - abundance of prism faces.

Bladed - like a wedge what stress is and what causes it knife blade Dendritic - tree-like growths Botryoidal - smooth bulbous shapes Examples of questions on this material that could be asked on an exam Define the following as they relate to crystal forms: (a) Pedion, (b) pinacoid, (c) prism, (d) pyramid, (e) dipyramid, octahedrn, (f) dodechahedron.

What is the difference skin disease vitiligo a closed form and an open form. What is a zone and what notation do we use to indicate a zone or a direction in a crystal. Given the symmetry of a crystal and a what stress is and what causes it symbol, be able to determine the number of faces that occur in the form (as what stress is and what causes it the example tables, above).

What is the difference between a continuous vectorial property and a discontinuous vectorial property.

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