  Colloidal systems offer unique opportunities for the study of phase formation
and structure since their characteristic length scales are accessible to
visible light. As a model system the two dimensional assembly of colloidal
magnetic and non-magnetic particles dispersed in a ferrofluid (FF) matrix is
studied by transmission optical microscopy. We present a method to
statistically evaluate images with thousands of particles and map phases by
extraction of local variables. Different lattice structures and long-range
connected branching chains are observed, when tuning the effective magnetic
interaction and varying particle ratios.
