'''Carbonado,''' commonly known as the 'Black Diamond,' is a natural alluvial deposits in the porous than other diamonds. 

==Unusual properties==
Unlike other natural polycrystalline diamonds, carbonado has no mantle-derived inclusions and its isotope value is very low. Additionally, carbonado  exhibits strong luminescence (photoluminescence and cathodoluminescence) induced by nitrogen and by vacancies existing in the crystal lattice. Analysis of the luminescence suggests that radioactive inclusions existed in the formation process of carbonado. These and other characteristics that separate  the carbonado from other diamonds have led to questions as to the carbonado's origin.

==Early theories on origin==
The origin of carbonado is controversial, with several hypotheses proposed:
#''Direct conversion of organic carbon under high-pressure conditions (the Earth's interior.)'' This is the standard, geological process of diamond formation. The problem with this hypothesis is that, were carbonado formed by phase transformation of organic graphite inside the Earth, they would be found all over the world. However, carbonado appears only in the Central African Republic and Brazil, in areas that are far from other diamond deposits.
#''Shock metamorphism induced by meteoritic impact at the Earth's surface.'' According to this hypothesis, carbonado were created by meteoric impact. The problem with this hypothesis is that shock-induced natural polycrystalline diamonds usually have hexagonal diamond (lonsdaleite) inside the samples, and carbonado does not. 
#''Radiation-induced diamond formation by spontaneous fission of uranium and thorium.'' The problem with this hypothesis is that the energy of radiogenic fission is too small to create polycrystalline diamonds of the large grain size of carbonado (up to 500 micrometers).

==Extraterrestrial origin==

A team of U.S. geologists have published evidence relating to a different origin of these black diamonds: interstellar space. They have found that black diamonds contain trace elements of nitrogen and hydrogen which they claim are sure indicators of an extraterrestrial origin.

The study published in 2006 by Stephen Haggerty and Jozsef Garai, of Florida International University, analyzed the hydrogen in black diamond samples using infrared-detection instruments at the Brookhaven National Laboratory. The researchers found that the chemical properties of carbonado indicated that the mineral formed in a supernova explosion that took place prior to the formation of our Solar System. 

Il '''carbonado''', chiamato anche ''diamante nero'', è un mantello e il suo valore di isotopo del carbonio è molto basso.

Mostra una forte radioattive.
L'origine del carbonado è controversa e sono state proposte diverse ipotesi ma che mostrano numerosi limiti.

Recentemente uno studio sofisticato sull'origine del carbonado sembra escludere che le condizioni terrestri possano essere compatibili con la sua formazione quanto con le condizioni che si creano durante una esplosione di una supernova.

Tramite la radiazione di sincrotrone all'infrarosso sono stati analizzati l'azoto e l'idrogeno contenuti in traccia in questo materiale.
L'analisi, ad opera di alcuni ricercatori dell'Università internazionale della Florida e dell'Università Case Western Reserve, dimostrerebbe la formazione di questi diamanti in un ambiente interstellare ricco di idrogeno, quindi al di fuori del sistema solare o prima della formazione dei pianeti. 
Successivamente i carbonado sarebbero stati incorporati all'interno di corpi solidi caduti sulla Terra come meteoriti.

Questo tipo di diamanti sono utilizzati in diversi modelli e creazioni nell'industria dei gioielli ma trovano più frequentemente applicazione nel settore industriale.