**2. Magnesium borate minerals**

As being notable magnesium compounds, magnesium borates mainly include the atoms of Mg, B, O; however, other types of elements may be included according to the reserves they are mined. According to the conditions they formed in nature or fabricated in the laboratory, the magnesium borates can include crystal waters and/or hydroxyl groups. Therefore, this type of magnesium minerals can be classified as hydrated or dehydrated forms. The common examples of identified magnesium borates and their crystal systems are presented in **Table 1**.


### **Table 1.**

*Identified magnesium borates and their crystal systems [4].*

*Magnesium Borates: The Relationship between the Characteristics, Properties, and Novel… DOI: http://dx.doi.org/10.5772/intechopen.104487*

### **Figure 1.**

*The examples of boron-oxygen linkages B(3)-O and B(4)-O.*

The arrangement of functional groups in the molecule determines the properties of magnesium borate [5]. As a chemical compound, magnesium borates mainly include the functional groups of three and four coordinated borate anions (B(3)-O and B(4)-O) connected to the magnesium atoms (**Figure 1**). The typical symmetric and asymmetric stretching in a molecule can be determined by Fourier-transform infrared spectroscopy (FT-IR) and/or Raman Spectroscopy.

Spectral analyses result of Admontite (MgB6O107H2O) samples prepared at different reaction times in hydrothermal conditions were presented in **Figure 2**. In FT-IR analyses of magnesium borates, the spectrum begins with the peak around 3500 cm<sup>1</sup> which indicates the crystal water for the hydrated compounds. The region above the 1600 cm<sup>1</sup> is generally called as "free H2O zone". The effects of hydroxyl anions are seen as "bending of hydroxyl groups in plane" and "bending of hydroxyl groups out of plane". The peaks between 1400 and 1200 cm<sup>1</sup> indicate "bending of hydroxyl groups in plane" whereas the peaks between 950 and 750 cm<sup>1</sup> are related with the "bending of hydroxyl groups out of plane". The stretching between boron and oxygen atom is commonly seen between 1600 and 650 cm<sup>1</sup> . The peaks in the region of 1600– 1400 cm<sup>1</sup> are related with the "asymmetric stretching of B(3)-O". "Asymmetric stretching of B(4)-O" can be explained with the peaks in the range of 1200–950 cm<sup>1</sup> . The peaks at the lower wavelength values of 750 cm<sup>1</sup> can be interpreted with the "bending of B(3)-O" [6–8].

### **Figure 2.**

*Spectral analyses result of Admontite prepared at different reaction times (a) FT-IR spectra, and (b) Raman spectra [6].*

In Raman analyses of magnesium borates, the characteristic peaks are seen in the wavelength region of 1200–250 cm<sup>1</sup> . The peaks between 1200 and 1050 cm<sup>1</sup> are interpreted with the "asymmetric stretching of B(4)-O". "Symmetric stretching of B(3)-O" and "symmetric stretching of B(4)-O" are seen in the range of 1050–900 cm<sup>1</sup> and 900–750 cm<sup>1</sup> , respectively. For the hydrated forms of magnesium borates, the stretching for polyanion of [B6O7(OH)6] <sup>2</sup> and [B3O3(OH)4] <sup>2</sup> is seen between 750 and 620 cm<sup>1</sup> . The "bending of B(3)-O" and "bending of B(4)-O" can be seen in the Raman shift wavelength ranges of 620–500 cm<sup>1</sup> and 500–250 cm<sup>1</sup> , respectively [6, 7, 9].
