Advanced nuclear reactor designs using more complicated and heterogeneous geometries warrant prcise modeling of the neutron transport phenomenon. The use of Method of Characteristics (MOC) with unstructured meshing renders an accurate representation for tracking the neutron transport in such heterogeneous media. The code DIAMOND is being developed for neutronic analysis of two-dimensional rectangular lattice/core problems using MOC. The problem of interest, represented by Constructive Solid Geometry (CSG) based processing module, is divided into unstructured meshes using Constrained Delaunay Triangulation (CDT). Search based ray tracing is used for laying down global cyclic tracks. The results from this code for a variety of benchmark problems have been validated against those obtained from other methods/codes. A performance comparison between triangular and traditional unstructured meshes is also presented. This paper provides a description of DIAMOND; equations governing the MOC formulation, the geometrical and meshing aspects along with its application to various benchmark problems.