A pictorial guide of cored rocks in the Waikato coal fields, New Zealand, with associated geotechnical and envirotechnical characteristics, has been prepared. The methodology, results (including facies interpretation) and use by mining personnel are discussed in this paper. Rock coring is widely conducted in most of the world's active coal fields. This exploration method, although the most costly, is the most complete record of the subsurface geology at any particular location. Unfortunately, much of this potentially valuable information is lost due to the incomplete description of the rock recovered from the core hole. In some cases, the description is adequate, but errors and confusion may arise from a lack of uniform terminology. It is the objective of this guide to provide a standard base for core description with a consistent set of terms to describe the rock and coal core. The guide contains a set of colour photographs of cores of the common rock types and coal in the Waikato coal measures. Each sample is given a name and a three- or four-digit number, which convey characteristics such as the grain size, colour, and sedimentary structure. The photographs are grouped into major classes that are accompanied by short texts describing the properties that are useful in differentiating rock types. (C) 2002 Published by Elsevier Science B.V.