Carbonado
Carbonado ( Spanish for " carbon" ), often called black diamond, is a very rare variety of the mineral occurring polycrystalline diamond.
As a composite of many small diamond crystallites, porous aggregate of predominantly irregular - rarely würfeliger rounded würfeliger - Form carbonados contain many impurities such as carbon or graphite, various metal oxides, as well as potassium, aluminum-or silicon-containing minerals. As a further pore filling iron, nickel, chromium, copper, magnesium, beryllium, calcium, and sometimes still found. According to various researchers view but they were not introduced until after the creation of the carbonados and therefore can not be used to explain its genesis. These admixtures are also responsible for the dark gray or rust brown to black color.
Special Features
The size of the individual units fluctuates generally between 0.001 and 0.2 millimeters. Previously, it was found only once a Carbonado of exceptional size, even surpassing the famous Cullinan diamond. The Carbonado do Sérgio was discovered in 1905 in the area around Lençóis (Bahia) and had a weight of 3167 carats ( Cullinan: ~ 3.106 carats).
The density of Carbonado varies from 3.1 to 3.4 g / cm ³ ( Location: Macaúbas Basin). The Stephen E. Haggerty in 1998 examined carbonados unknown origin even had only a density of 2.8 g / cm ³. In diamonds, the density contrast is usually about 3.515 g / cc. Although small in comparison to the hardness of a diamond density carbonados is so high that he can not be edited with normal grinding methods. One group of researchers K. De Corte succeeded in 2004, only with a laser to form carbonados and polish. Its great hardness and in the process according to his excellent abrasive characteristics would be of great benefit for the technical industry. However, a large-scale industrial use as an abrasive is contrary be exceedingly rare occurrence. The primary goal of the research is therefore to unravel the formation conditions of carbonados and these produce when possible synthetic.
History
The earliest reports of Carbonadofunden and their assignment to the diamonds come from in 1840 " Chapada Diamantina " (Bahia), where they were washed out of the local river soaps.
After the discovery of large diamond deposits in South Africa attracting Brazilian diamonds collapsed while, but the demand of carbonados remained almost unchanged due to its highly valuable for industrial properties. Thus, the proportion rose to carbonados to 60 to 70% compared to total production ( as of 2004). Bahia today promotes neither diamonds nor carbonados. With the declaration of the entire region to the national reserve, any mining activity was strictly prohibited.
In January 2011, the new Black Diamond extension of the German Mining Museum Bochum received a Carbonado weighing ~ 3.4 carats. The jeweler Michael Mauer explained his gift humorous with the words " In the Black Diamond has a black diamond " and that he would be here on coal, have learned here to make " coal " and therefore could give something back to coal to the city.
Education and Locations
Since a diamond is formed under terrestrial conditions only at great depths under high pressure and high temperature, which has a compact structure in the known form of the result was suspected early on that not Carbonado originated on the Earth. His pores contain hydrogen and are also filled with quartz, which made a study of the infrared spectrum to clarify its origin impossible so far. However, Jozsef Garai and Stephen Haggerty of Florida International University found a way: you zermahlten samples of Carbonado and removed the quartz using hydrochloric and hydrofluoric acid. Subsequent irradiation with intense synchrotron radiation, it was found that the spectrum of the carbonados of diamonds from meteorite is very similar.
In fact, however, there are still only speculate about the exact formation conditions of carbonados, more or less based on the composition of the previously investigated samples and the geological properties of the respective localities.
Particularly striking is that the " black diamonds " are never isolated but always together with normal diamonds found. On the other hand you have not met her in kimberlites or related rocks, the typical host rock of diamonds, to, only secondarily in soaps. For example, the region of Macaúbas River in Minas Gerais by glacial ( Pleistocene ) Sedimentation before about 950 million years ago (after Pedrosa - Soares et al., 2000) emerged. Moreover, since in Macaúbas Basin next to diamonds and carbonados also chrysoberyl, Monzanit, staurolite and almandine were found that their well-known formation conditions, according to can not have originated in the present there geological formations, only one transport comes Glacial age from north-north- westerly direction (Bahia) followed by alluvial accumulation in question.
As localities have been a total of only Diamantina and Lençóis, Bahia; the region of the Macaúbas River (also Macaúbas lineup, formerly Macahúbas ) in Minas Gerais; Ubangui in Zaire lowlands; Western Australia; Venezuela; English Guiana; North China; Borneo; as well as Sakha ( Yakutia) in Russia known.