This book is the result of numerous analytical works carried out in connection with the very rich geology of the Massif Central (France). It aims to determine the nature and origin of certain rocks discovered in nature and presenting aspects or colors not explained to date. Particular attention was paid to the genesis of the aetites also called "Stones of eagles". This work also retraces the expertise of materials from ancient constructions (Roman period). The aim was to determine the types of building materials used and their origins. The results of the analysis of the rocks and minerals found in the environment of a mammoth skull allowed to better understand its presence in the sediments. The analyses of the minerals were performed by X-ray diffraction (XRD). The first part of this book will give the theoretical and technical bases of this type of analysis.