In the Soviet Union the first diamond placers worth mining were revealed in 1949 on the central Siberian Plateau, which lies in Yakutia between the Lena and Yenisei rivers. A few years later, in 1954, the young mineralogist L. Popugaeva, while following garnet gravel, stumbled on a diamond-bearing kimberlite pipe diamond engagement rings , which she named Sarzina. Other mines opened up since then are the Mir, the Udatschnaya, and the Aichal. Their gangue material consists of kimberlite which, despite its many varieties, resembles the basaltic kimberlites of South Africa.

The Siberian "pipes" yield mainly industrial diamonds in ideal sizes; but just recently very large gem diamonds have also come from them; in 1967 the Maria diamond of 106 carats, in 1968 the Stalingrad, which weighed 166 carats, and, shortly afterward, from the same mine near Mirny, a 236-carat diamond.

Although diamond is not only the gemstone best known to the layman but equally the most intensively investigated mineral, diamond wedding rings t nevertheless continues to pose scientists more puzzles than any other substance. But never, not even in the face of their sober and factual findings, does it lose a jot of its magic. On the contrary, through precise examination of the material the true miracle of its nature was first unfolded. Diamond is the only precious stone which consists of a single element, namely quadrivalent carbon (C).

It differs from common graphite and coal only in the extraordinarily close cubic space packing of the C atoms, which, together with the strong cohesion of its bonds, is responsible for its unequalled hardness (which, at 10, occupies the top place on the Mohs hardness scale); and in the three stone diamond rings surpassing refraction of light, whence its dazzling brilliance and strong dispersive power originate. Because of the relative lightness of carbon, its specific gravity amounts only to 3.52. The form of the unit cell of diamond, which crystallizes in the cubic system, produces a tetrahedron (a body bounded by four triangular faces).

The commonest growth habits are the octahedron (bounded by eight triangular faces), the cube, and the rhomb-dodecahedron (bounded by twelve rhomb-shaped faces). The cutting industry noticed long ago that misshapen diamond crystals can be cleaved more easily and better than well-formed to perfectly formed ones; however, it was reserved to scientific research to recognize that a distinguishable state of the included trace elements was the cause of this ambivalent behavior. These elements were ascertained to be responsible for the colors and other optical and electronic properties of diamond, on account of which it has become a material with many uses in modern technology. The most widespread trace element is nitrogen. It is found in all diamonds of Type I, while those of Type II have none.

These two structurally distinct diamond types fall again, in their turn, into two subclasses. In .diamonds of Type la, in which the proportion of nitrogen to carbon is high (1:1,000), the nitrogen atoms unite in groups of minute platelets. Such diamonds are colorless. In diamonds of Type lb the nitrogen atoms are built into the diamond structure as substitutions in disperse (finely distributed) form and give rise, vintage engagement rings according to their quantity, to the brown, yellow (as in the Florentine and the Tiffany), and green (for example, the Dresden Green) colors. All diamonds of Type I are characterized by good, well-developed crystal forms and poor cleavage. The nitrogen-free Type II diamonds give themselves away externally by their misshapen forms, on which hardly a single crystal face can be recognized, and by their easy cleavage.