Mineralogical studies of platinum-group minerals (PGM) made during the period 1970-1995 are compiled in this paper for PGM obtained from platinum- and gold-bearing placer deposits of fifteen countries. A total of 3399 quantitative electron microprobe analyses of 37 different PGM are presented, together with analytical data plotted on compositional diagrams. The data reflect the dominance of Pt-Fe alloys (1723 analyses) and Os-Ir-Ru-Pt alloys (976 analyses) in the placers. The platinum-group element (PGE) alloys, as well as some other PGM, generally occur as grains less than one millimetre in size.

Ruby as a natural gemstone has an early history in which its colorful properties [1] were much valued in ornamental and symbolic jewelry by potentates and other persons of power and prestige [2,3]. This appreciation has extended into latter times and more so into the more general populace. It is an important gem for scientific study [4] and for exploration quests to find new ruby deposits [5,6].

The purpose of petrology is to understand the conditions of the formation of rocks. The first stage of this approach is to describe and classify the rocks; that is the subject of petrography. Many characters can be used: density, hardness, colour, structure (on the scale of the outcrop), texture (on the scale of the sample or of the microscope), mineralogical composition, chemical composition, speed of propagation of the waves, etc. Among all the characters, the mineralogical composition is certainly the most important: it allows us to, more or less, accurately foresee the other characters and it can be used to determine the very conditions of the formation of rocks. Indeed, the nature and chemical composition of the minerals in a rock obey stricter laws, since the formation temperature was higher

Literally, “Mineralogy” means science of minerals.

The term “mineral” was coined in the late Middle Ages; it is derived from the Medieval Latin word mina = shaft (minare = to mine). The antique people, e.g., the Greeks and Romans, only used the word “stone”. Special attention was dedicated to precious stones, distinguished by their lustre, colour and hardness, which were highly estimated by the old civilised nations already in pre-Greek times.