Shimmering diamonds are not just earthly in origin. They can also be interstellar and meteoritic. From the depths of the earth to the expanses of the sky, it seems that, diamonds are not only forever but also all-pervasive
DIAMONDS are formed in more ways than
one. While it was believed earlier that
the beautiful crystals were retrieved
from deep mines of igneous or metamorphic rocks of the mantle formed
under conditions of high temperature
and pressure, new research reveals that
there are other ways by which they are
formed in nature.
Meteorite impaction on the earth's
surface is one instance which has led to
the formation of these precious stones.
Work conducted by R M Hough and
others from the department of earth sciences at the Open University in Milton
Keynes, UK, now adds another theory
regarding the origin of these surface diamonds. It is believed that diamonds
were present in the parent meteorite
and were expelled onto the earth's surface as a result of the impact. Earlier
studies have shown the presence of these
crystals in leaded meteorites and urelites. It was also assumed that diamonds
in a meteorite originate due to the high
gravitational pressure exerted on it during its fall and may have interstellar origins (Nature, Vol 378, No 6552).
Recently, scientists discovered tiny
diamonds, identified from an elusive
noble-gas bearing component in chondritic (spheroidal mineral grain bearing) meteorites. The rare gas component gave them away as being interstellar in origin, formed due to vapour condensation in stellar atmospheres.
Hough et al conducted their study
on material collected from the 23 km
diameter Reis crater in Germany, where
they found small quantities of cubic and
hexagonal diamonds alongwith cubic
diamonds interspersed with silicon carbide. The discovery of such diamond
composites is the first of its kind,
formed by undergoing condensation in
the hot vapour cloud of the impact.
Impact diamonds have also been
found in clay, marking the boundary
between the Cretaceous and Tertiary
periods when the earth was bombarded
by a large number of meteorites. Carbon
and nitrogen isotopic data revealed
these diamonds to have been formed
due to impact or from within the
fireball. The chemical structure and
isotopic markings of these impact associated polycrystalline diamonds is distinct. They preserve the macroscopic
crystal layout of the graphite crystals
from which they originate due to shock
metamorphism.
Another rare and unusual form of
polycrystalline black diamonds have
been found in the sedimentary formations in Bahia, Brazil and in Ubangi,
Central African Republic. These formations are called carbonados, which are
extremely hard polycrystalline aggregates. Enclosed within their porous
matrix of randomly arranged crystals
are octahedral and cubic diamonds. The
mechanism of formation of these diamonds is not yet clear, though suggestions range from their origin as carbon
subduction in the mantle, to shock
metamorphism during impact of irradiation of organic matter.
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