DIAMONDITE
Carbonado diamondites (small specimen at top: 4.05 carats and 9x9x6 mm in
size; medium-sized specimen at left: 4.07 carats and 10x13x7 mm in size; large
specimen at right: 5.09 carats and 12x6x6 mm in size).
Diamondites are rare, polycrystalline, nearly monomineralic diamond rocks.
The term "diamonds" refer to individual mineral crystals. The
term "diamondites" refer to diamond rocks. The three
diamondites depicted here are a variety referred to as "carbonados"
in the diamond trade. Carbonados are typically a dark brown to blackish
color. The shiny luster seen in the specimens below is typical for carbonados
(adamantine luster). Individual diamond crystals in carbonado diamondites
are exceedingly small, typically <20 m.
Carbonados are also characterized by having obvious porosity in all portions of
the rock (see pits in specimens shown above).
Despite a relative abundance of published research,
the origin of carbonado diamondites is still unresolved. Some workers interpret
them as being crustal in origin. Some consider them to have a mantle
origin. Some suggest that they are impact-generated. Recent
research has indicated that carbonado diamondites are extraterrestrial -
extrasolar, in fact (apparently supernova-generated).
True carbonado diamondites have only been recorded
from Brazil and the Central African Republic (CAR). Considering South America
& Africa were physically connected for a long time while a part of the
ancient Gondwana continent, these two carbonado occurrences may ultimately
represent one deposit. The specimens shown above are from the CAR.
In the CAR, carbonado diamondites are recovered from
modern to subrecent alluvial gravels (placer deposits) below the topsoil.
They are only found in & immediately adjacent to the outcrop belt of the
Carnot Formation (Cretaceous). The Carnot Formation is an ancient fluvial
& lacustrine siliciclastic unit that hosts scattered diamonds &
carbonados. Upon weathering & erosion, any included diamonds in the
Carnot Formation enter modern river systems' sediment loads.
Age:
carbonado diamondites are exceedingly old. Published research indicates they
are 3.2 billion years old (mid-Mesoarchean).
Locality:
unrecorded locality in the "Bangui region" (area between the cities
of Bangui and Berberati), southwestern Central African Republic, central
Africa.