Crystal structure

Crystal structure
From Wikipedia, the free encyclopedia

In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry. Patterns are located upon the points of a lattice, which is an array of points repeating periodically in three dimensions. The points can be thought of as forming identical tiny boxes, called unit cells, that fill the space of the lattice. The lengths of the edges of a unit cell and the angles between them are called the lattice parameters. The symmetry properties of the crystal are embodied in its space group.
 
SEM micrograph of surface of a colloidal crystal. Structure and morphology consists of ordered crystallites, grains or domains of particles as well as interdomain lattice defects in the form of grain boundaries.

Fabric (geology)

Fabric (geology)
From Wikipedia, the free encyclopedia

In geology, a rock's fabric describes the spatial and geometric configuration of all the elements that make it up.[1].

Types of fabric

• Primary fabric – a fabric created during the original formation of the rock e.g. a preferred orientation of clast long axes in a conglomerate, parallel to the flow direction, deposited by a fast waning current.
• Shape fabric – a fabric that is defined by the preferred orientation of inequant elements within the rock, such as platy or needle like mineral grains. It may also be formed by the deformation of originally equant elements such as mineral grains
• Crystallographic preferred orientation – In plastically deformed rocks the constituent minerals commonly display a preferred orientation of their crystal axes as a result of dislocation processes.
• S-fabric – a planar fabric such as cleavage or foliation, when it forms the dominant fabric in a rock, it may be called an S-tectonite
• L-fabric – a linear fabric such as mineral stretching lineation where aggregates of recrystallised grains are stretched out into the long axis of the finite strain ellipsoid, where it forms the dominant fabric in a rock, it may be called an L-tectonite.
• Penetrative fabric – a fabric that is present throughout the rock, down to the grain scale.

Primary fabric in anorthosite intrusion, Rogaland, Norway 

Isostasy

From Wikipedia:

Isostasy (Greek isos = "equal", stásis = "standstill") is a term used in geology to refer to the state of gravitational equilibrium between the earth's lithosphere and asthenosphere such that the tectonic plates "float" at an elevation which depends on their thickness and density.