Can someone explain a 'phase' as it relates to matter?

Question

I don't really understand all the definitions wikipedia and other websites give; what's the distinction between a phase and a state of matter? Tell me clearly what a phase is and give examples please. Thanks in advance.

Answer 1

In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i.e. density, crystal structure, index of refraction, and so forth).

Phases are sometimes confused with states of matter, but there are significant differences. States of matter refers to the differences between gases, liquids, solids, plasma, etc. If there are two regions in a chemical system that are in different states of matter, then they must be different phases. However, the reverse is not true — a system can have multiple phases which are in equilibrium with each other and also in the same state of matter. This difference is especially important when considering the Gibbs' phase rule, which governs the number of allowed phases.

Answer 2

The state of matter refers specifically to the solid/liquid/gas/plasma distinction.  By contrast, the phase of matter can describe any system where one combination of chemicals can take multiple, physically distinct forms.  In a crystal, for instance, the atoms might arrange in either a cubic or a hexagonal crystal structure.  Crystals of each structure would both be in the solid state, but they would be in different phases.  Another example would be a freshly blended mixture of oil and water.  Parts of the mixture would be blobs of oil with a little bit of water suspended in them, and other parts would be regions of water with a little bit of oil mixed in.  Both are liquids, but the phases are different.