Agglomeration occurs in many industrial and biological systems, but is still poorly understood. This paper addresses part of the problem by looking at the structure of the agglomerates themselves. The rate of agglomeration in a precipitating system depends upon many factors, one of which is the efficiency of the collision process between the crystals. Having found a reliable new method of producing calcite agglomerates, their structure is analysed by scanning electron microscopy and transmission electron microscopy with the aim of determining whether certain types of collision have a greater or smaller chance of forming a stable agglomerate.