Amphiboles: Historical Perspective

Abstract

For centuries, asbestos and jade were the only known representatives of the group of minerals called amphiboles. In the XVIII century, rock minerals with naturalistic descriptions and little more than semiquantitative chemical analyses were also considered, while the XIX century saw an enormous number of goniometric determinations and chemical analyses to try to classify the many species that were gradually being discovered. Chemical analyses that were precise and without preconceptions were developed in the early XX century, but it was mainly X-ray diffraction that helped to clarify the nature of this group of minerals. The present discussion of the evolution of knowledge about the amphiboles stops at the second world war. In the second half of the XX century, there has been great technical progress in mineralogical research, especially in the field of spectroscopy. This has led to detailed crystallochemical knowledge of the amphiboles, which has also allowed their use for the solution of petrological problems. German miners of the early XVIII century gave the name Hornblende , i.e., “dazzling horn,” to a mineral that had a toughness similar to that of horse hooves and did not contain useful metals. A century later, Rene J. Hauy decided to give it a different name, Amphibole , i.e., ambiguous, because it often had a similar appearance but a different composition. Today, we know that amphiboles are a complex group of rock-forming minerals with numerous lattice sites that can host many different constituents; indeed, it has jokingly been defined as a “waste basket.” It is hoped that this note will give the reader an idea of how hard the road has been for researchers on amphiboles. It started with the simple description of the external appearance of these materials and has led today, at the beginning of the third millennium, to the acquisition …