Mixing of liquids A and B and subsequent phase separation
When mixed, oil and vinegar will phase-separate
A phase diagram for two isotopes of helium, showing at bottom a range of temperatures and ratios at which they will phase-separate.
Phase separation is the creation of two distinct phases from a single homogeneous mixture. The most common type of phase separation is between two immiscible liquids such as oil and water. Colloids are formed by phase separation, though not all phase separation forms colloids - for example oil and water can form separated layers under gravity rather than remaining as microscopic droplets in suspension.