Prove that the volume of a tetrahedron with coterminous edges \( \mathbf{a}, \mathbf{b}, \mathbf{c} \) is \( \frac{1}{6} |\mathbf{a} \cdot (\mathbf{b} \times \mathbf{c})| \). Hence, find the volume of tetrahedron whose coterminous edges are \( \mathbf{a} = \hat{i} + 2\hat{j} + 3\hat{k} \), \( \mathbf{b} = -\hat{i} + \hat{j} + 2\hat{k} \), and \( \mathbf{c} = 2\hat{i} + \hat{j} + 4\hat{k} \).