What are microcultures formed on?

Answer 1

A social group that shares distinctive traits, values, and behaviors that set it apart from the parent macroculture of which it is a part. Microculture seems to imply a greater linkage with the parent culture and often mediate the ideas, values, and institutions of the larger political community.

Simplified:
Age, Class, Race, Gender. Anything you can do to group people together. Could even be height, hair colour, athleticism... whatever you can think of to group objects together is a microculture.