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,
Chlorine causes: extreme inertness and reluctance to participate in chemical reactions (the noble gases, with the exception of xenon in the highly unstable XeCl and XeCl); extreme nuclear instability hampering chemical investigation before decay and transmutation (many of the heaviest elements beyond bismuth); and having an electronegativity higher than chlorine's (oxygen and fluorine) so that the resultant binary compounds are formally not chlorides but rather oxides or fluorides of chlorine. Chlorination of metals with Cl usually leads to a higher oxidation state than bromination with Br when multiple oxidation states are available, such as in MoCl and MoBr. Chlorides can be