Sentence:  <WSD>Carbonados</WSD> are polycrystalline diamond aggregates of generally irregular shapes that have been observed in placer deposits and low-grade metamorphic rocks of mainly Brazil, Russia, South Africa, Ukraine, Venezuela, and the Central African Republic. [...] Smith and Dawson (1985), consequently, suggested that <WSD>carbonados</WSD> could have been formed as a consequence of Precambrian impact events into carbon-bearing crustal rocks. All other traces of these impacts and the related impact structures apparently have been eroded, and only the <WSD>carbonados</WSD> had survived erosion and were then incorporated into sedimentary rocks. 
Meaning of the word marked with <WSD> tags:  A dark, non-transparent, impure form of polycrystalline diamond (also containing graphite and amorphous carbon) used in drilling.