Assessment of the molecular structure of the borate mineral boracite Mg _3B _7O _(13)Cl using vibrational spectroscopy

摘要

Boracite is a magnesium borate mineral with formula: Mg _3B _7O _(13)Cl and occurs as blue green, colorless, gray, yellow to white crystals in the orthorhombic - pyramidal crystal system. An intense Raman band at 1009 cm ~(-1) was assigned to the BO stretching vibration of the B _7O _(13) units. Raman bands at 1121, 1136, 1143 cm ~(-1) are attributed to the in-plane bending vibrations of trigonal boron. Four sharp Raman bands observed at 415, 494, 621 and 671 cm ~(-1) are simply defined as trigonal and tetrahedral borate bending modes. The Raman spectrum clearly shows intense Raman bands at 3405 and 3494 cm ~(-1), thus indicating that some Cl anions have been replaced with OH units. The molecular structure of a natural boracite has been assessed by using vibrational spectroscopy.