| In recent 20 years,the domestic researches about Brazilian diamonds are few.In order to detailed study the micro-morphology and spectral characteristics of Brazilian diamond,lots of measurements and analysis were carried out,such as photographic microscope,Diamond ViewTM,Infrared spectrum,Raman spectrum,and UV-visible spectrum.Under microscope,it is found that the main color of Brazilian diamond is colorless,gray and yellow.The crystal forms are mainly rhombic dodecahedron,irregular polyhedron,and some flat shapes.The internal inclusions are abundant,and the surface cracks and pits are often filled with other minerals.There are lots kinds of surface features,such as various morphological growth hills,triangular,hexagonal or irregular erosion pits,plastic deformation slip lines,etc.Some samples have yellowish brown and green spots on the surface,and the proportion of yellowish-brown spots is bigger.Spectrometric analysis shows that Brazilian diamonds are dominated by type Ia AB with a content of more than 90%,and have a small amounts of type Ia B and?a.The nitrogen content is between 400?1700?g·g-1,and the average nitrogen content is 880?g·g-1.The conversion rate of B color center is between 15%?66%,accounting for an average of 45%.Brazilian diamonds have the characteristics of high nitrogen contents and low-medium nitrogen accumulations.The Raman intrinsic peak position shifted by 1?2 cm-1 to high frequency compared with the standard 1332 cm-1 and the FWHM is up to 11 cm-1,which demonstrate Brazilian diamonds have residual stresses and poor crystallinity.The epigenetic inclusions of Brazilian diamonds include calcite,goethite and quartz,and the surface minerals are graphite and secondary sulfate sedimentary minerals.Diamond ViewTM analysis shows that Brazilian diamond may grow in two kinds of growth environments.Diamonds with flat crystals have stable growth environment,which have low nitrogen in the early stage and apparent more nitrogen in the later period.Diamonds with original crystal or irregular other crystal forms have unstable growth environment and multi-stage growth characteristics.Ultraviolet-visible light spectroscopy analysis shows that almost all Ia AB type diamonds,which emit blue fluorescence,have the absorption of N3 at 413 nm.The green or green-blue samples mostly have the absorption of GR1 color center at 741 nm.At the same time,it is confirmed that N3 is not the only cause of blue fluorescence. |
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