Diamond's 2 billion year growth charts tectonic shift in early Earth's carbon cycle

Gem quality diamond from Letlhakane, containing multiple orange garnets

[Credit: M. Gress, VU Amsterdam]

A composite of 9 catholuminescence images recording the growth history in an individual gem quality diamond 3 mm in

diameter. The general tree ring structure defined by the different blue colours record variations in the nitrogen content

of the diamond. Black equates to less than 10 parts per million and the brightest colours to ~500 ppm. The diamond

has a complex history with multiple periods of growth. The irregular centre is surrounded by regular but rounded

growth zones due to the diamond suffering resorption. This occurs when a diamond is eaten away by fluids deep

in the Earth’s interior (> 150 km). Dating of inclusions from different growth zones allows the time

taken for diamond growth to be determined [Credit: M. Gress, VU Amsterdam]

A selection of unprocessed inclusion-bearing gem quality diamonds from Letlhakane. The dark areas surrounding the

shiny metal like inclusions (sulphide) are graphite in cracks that from due to the differential expansion of the

sulphide and diamond when brought to the surface from a depth of over 150 km. Bottom left diamond

contains an orange garnet and a green clinopyroxene [Credit: M. Gress, VU Amsterdam]

A plate cut through the centre of a gem quality diamond from Letlhakane, containing multiple orange garnets

and green clinopyroxenes. Fractures in the diamond caused by the laser cutting and subsequent polishing

[Credit: M. Gress, VU Amsterdam]

An orange garnet exposed at a broken diamond surface. Note the well-developed crystal face at the top left

that implies that the diamond imposed its crystal form on the garnet during growth of the garnet

[Credit: M. Gress, VU Amsterdam]

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