INVESTIGATIONS OF DIAMONDS FROM MINAS GERAIS (BRAZIL) BY VIBRATIONAL SPECTROSCOPY
Type Ia and type II diamonds have been described among 91 investigated stones from Minas Gerais State (Brazil) through infrared activity of nitrogen centres. Four different type Ia diamond populations have been defined from their nitrogen aggregation histories. The discrimination method is based on fact that platelet (D defect) develop as A centres evolve to B centres in mantle under very well controlled conditions of time and energy. Ratio B/A versus D diagram seems to indicate that nitrogen aggregation behavior of each group can be mathematically described by a first degree equation. Additionally, pyrope and forsterite included in diamonds have been analyzed by Raman spectroscopy and revealed peridotitic mantle mineralogy under the southern São Francisco Craton.