As stated above, the electrical interaction between the atoms of a crystal determine its physical and chemical properties.Thus, classifying minerals according to their electrical forces will cause those species with similar properties to be grouped together. Atoms have a tendency to gain or lose electrons so that their outer orbitals become stable; this is normally accomplished by these orbitals being filled with the maximum allowed number of valence electrons.The physical and chemical properties of minerals are attributable for the most part to the types and strengths of these binding forces; hardness, cleavage, fusibility, electrical and thermal conductivity, and the coefficient of thermal expansion are examples of such properties.On the whole, the hardness and melting point of a crystal increase proportionally with the strength of the bond, while its coefficient of thermal expansion decreases.It is also used to make heavy-duty electrical contacts.Iridium was used in making the international standard kilogram, which is an alloy of 90% platinum and 10% iridium.
The electrical forces, called chemical bonds, can be divided into five types: ionic, covalent, metallic, van der Waals, and hydrogen bonds.
The photo below shows the iridium rich layer, which marks the demise of the dinosaurs. Harmful effects: Iridium is considered to be of low toxicity.
Iridium in powder form is a known irritant and is a fire hazard.
Classification in this manner is largely one of expediency; the chemical bonds in a given mineral may in fact possess characteristics of more than one bond type.
For example, the forces that link the silicon and oxygen atoms in quartz exhibit in nearly equal amount the characteristics of both ionic and covalent bonds.