11. Stress versus strain data should be obtained in both uniaxial and biaxial forms. 12. In an optical spectrum changbaiite is uniaxial positive and it can be biaxial . 13. It belongs in the biaxial group, because it is an orthorhombic mineral. 14. Earth is not a sphere, but an irregular shape approximating a biaxial ellipsoid. 15. The angle between the two axes is denoted by 2V . Vauxite is biaxial . 16. All minerals of the monoclinic, orthorhombic, and triclinic systems are biaxial minerals. 17. Biaxial minerals are further subdivided by optic sign.18. In sarabauite crystals this angle is obtuse, thus the mineral is biaxial negative. 19. Being triclinic, ulexite is optically biaxial . 20. Optically, this mineral is biaxial negative, meaning that it contains two optic axes.
