Assessment of the molecular structure of the borate mineral boracite Mg3B7O13Cl using vibrational spectroscopy

Boracite is a magnesium borate mineral with formula: Mg3B7O13Cl 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 B7O13 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. (c) 2012 Elsevier B.V. All rights reserved.