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While earlier investigations of carbonado focused on physical and chemical properties and synthesis, more recent studies have introduced dating techniques, high-resolution microscopy, spectroscopy, and an emphasis on origin (see Haggerty, 2014, for a more comprehensive view). As the porosity of an object increases, its apparent density decreases, because the voids take up more and more of the volume. Gurney et al., Eds., , Red Roof Design Publications, Cape Town, pp. The present study offers a detailed examination of about 800 carbonados from Brazil and the Central African Republic (figure 2), ranging from Figure 2. The carbonados in the left (118 ct) and center (16.2–52.2 ct) photos are from the Central African Republic, and those on the right (10.8–15.1 ct) are from Brazil. In carbonado, the number of exposed microdiamond cutting points increases with porosity. (1999) Constraints from luminescence on the history and origin of carbonado. Right: Separation of the microcontinent into two cratonic blocks, now Brazil and the Central African Republic, took place during the breakup of Gondwanaland about 180 million years ago."Figure 1. Left: The Congo–São Francisco island in southwest Rodinia, at approximately 1.1 billion years ago (Ga), is the only known site of carbonado that was originally deposited ca. Continental masses in Rodinia are underlain by ancient cratons approximately 2.5 to 4.0 Ga. A: Scene from Chapada Diamantina, the carbonado site in Bahia, Brazil. A: Scene from Chapada Diamantina, the carbonado site in Bahia, Brazil. Note the high density of pores, some of which are filled at the surface by crustal infiltrates, and the metallic luster of the glassy melt-like patinas. GIA Collection numbers 40108–40119; gift of Stephen Haggerty."Figure 3. This was a sought-after property that made carbonado more expensive by weight than diamond at the turn of the twentieth century (Haggerty, 2014). Calculated pore concentrations vary between 5% and 15% in volume.
Contact boundaries between pore-present and pore-absent surfaces are poorly defined, except in cases where patina crusts have splintered off where the contact is sharp, as seen in the lower-right images of figure 6 and in figure 7.
Four of the five largest diamonds reported from Brazil, ranging in weight from 726 to 3,167 ct, are carbonado (Svisero, 1995).
The largest of the five, the Sergio, recovered in 1905, is 61 ct heavier than the largest single-crystal diamond ever reported (the 3,106 ct Cullinan rough).
Models for its genesis are far-reaching and range from terrestrial subduction to cosmic sources.
Discovered in 1841 in Brazil, carbonado was named by Portuguese diamond prospectors for its resemblance to charcoal (Leonardos, 1937; Dominguez, 1996).