Full Text Search Mineral identification by keyword searching The carbonates and related nitrates and borates are common constituents of the earth's near-surface crust. At every corner of the triangle sits an oxygen atom. The threefold symmetry of the triangle explains the trigonal symmetry that many members of this class possess. As long as the triangles of the anionic group fall in a plane parallel with the plane of the triangle and all other bonds in the structure, when viewed perpendicular to this plane, are multiples of three, and are evenly separated from each other, the mineral will have a trigonal symmetry. As complicated as this seems it is in fact the simplest condition of the carbonates.
Simplicity often expresses the highest symmetry.
Although somewhat varied, this class' properties can be generalized more so than the other classes. Typical carbonates are transparent, lightly colored with a white streak, average to above average in density, soft with good to perfect cleavage, soluble to at least some degree in acidic solutions, and tend to originate in sedimentary and oxidizing environments with the exception of carbonatite igneous intrusions. Most of these common characteristics are due to the common chemistry the group shares and members that diverge from the norm do so because of the effects of metal cations such as lead, copper, manganese and iron. The Borate minerals as a whole are more complex in their structures than typical carbonates and could be considered their own class for that reason. For more discussion and a rather extensive list of borate minerals see the Borate Minerals page.