Iodine by mass action due to the precipitation of the insoluble salt. Iodine is the least abundant of the stable halogens, comprising only 0.46 parts per million of Earth's crustal rocks (compare: fluorine 544 ppm, chlorine 126 ppm, bromine 2.5 ppm). Among the eighty-four elements which occur in significant quantities (elements 1–42, 44–60, 62–83, and 90–92), it ranks sixty-first in abundance. Iodide minerals are rare, and most deposits that are concentrated enough for economical extraction are iodate minerals instead. Examples include lautarite, Ca(IO), and dietzeite, 7Ca(IO)·8CaCrO. These are the minerals that occur as trace impurities in the caliche, found in Chile,
Copper and halides. Both cuprous and cupric oxides are known. Among the numerous copper sulfides, important examples include copper(I) sulfide and copper(II) sulfide. Cuprous halides (with chlorine, bromine, and iodine) are known, as are cupric halides with fluorine, chlorine, and bromine. Attempts to prepare copper(II) iodide yield only cuprous iodide and iodine. Copper forms coordination complexes with ligands. In aqueous solution, copper(II) exists as [Cu(HO)]. This complex exhibits the fastest water exchange rate (speed of water ligands attaching and detaching) for any transition metal aquo complex. Adding aqueous sodium hydroxide causes the precipitation of light blue solid copper(II) hydroxide. A simplified