21. Its chemical formula is triclinic crystals. 22. Chabazite crystallizes in the triclinic crystal system with typically rhombohedral shaped crystals that are pseudo-cubic. 23. The related mineral parahopeite, which has the same composition but different crystal structure, is triclinic . 24. Triclinic , monoclinic and orthorhombic crystals have two optic axes, and are said to be biaxial.25. It is generally considered to be monoclinic, though optical studies have suggested it might be triclinic . 26. Its crystal symmetry was first assigned as orthorhombic, then as monoclinic, and finally as triclinic . 27. Kyanite is triclinic , while andalusite and sillimanite are both orthorhombic and belong to the dipyramidal point group. 28. Also the whole parallelepiped has point symmetry " C i " ( see also triclinic ). 29. It forms triclinic pinacoidal crystals which often occur as tubes or cylinders which are in fact rolled sheets. 30. In total there are six crystal families : triclinic , monoclinic, orthorhombic, tetragonal, hexagonal and cubic.
