Menu
Home
People
Places
Arts
History
Plants & Animals
Science
Life & Culture
Technology
Reference.org
Carnallite
open-in-new
<h2 id="background">Background</h2> <p><a href="/facts/Halides/ujYu8kGD">Halides</a> are <a href="/facts/Binary_compounds/pQ7zq0Cv">binary compounds</a>. They are composed of a <a href="/facts/Halogen/YeFgWHeA">halogen</a> and a metal ion. The crystal chemistry of halides is characterized by the <a href="/facts/Electronegativity/H7Vq7Uah">electronegativity</a> of halogen ions.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> This means that the dominant large ions are the Cl−, Br−, F−, or I−. These are easily polarized.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a><a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> The ions combine with similarly large but low valence and weakly polarized cations. The cations are mostly of the <a href="/facts/Alkali_metal/IkWbCLk2">alkali metal</a> group. Sylvite is a binary compound with the formula KCl. Sylvite precipitates first from mixed solutions of K+, Mg2+ and Cl−, leaving a brine enriched in magnesium from which the mixed halide carnallite then precipitates.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> </p> <h2 id="composition">Composition</h2> <p>Carnallite's chemical formula is <a href="/facts/Potassium/FWPwS7Rj">K</a><a href="/facts/Magnesium/XyIhd2FG">Mg</a><a href="/facts/Chlorine/y27UwYBM">Cl</a>3·6(<a href="/facts/Water/0lkXnJPK">H2O</a>). Synthetic carnallite crystal specimens can be produced from 1.5 mole percent KCl and 98.5 mole percent MgCl2·6H2O by slow <a href="/facts/Crystallization/oCUUG80k">crystallization</a> at 25 °C.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> Its density is 1.602 g/cm3.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> Carnallite can also be produced by grinding the combination of hydrated magnesium chloride and potassium chloride.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> </p> <h2 id="structure">Structure</h2> <p>The carnallite structure exhibits corner- and face-sharing. There is a network of KCl6 octahedra, with two-thirds of them sharing faces.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> Mg(H2O)6 octahedra occupy the open spaces within the KCl octahedra. The interatomic distance between Mg and H2O ranges from 0.204 to 0.209 nm,<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> with an average is 0.2045 nm.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> The interatomic distance between K and Cl ranges 0.317 to 0.331 nm.,<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> with an average of 0.324 nm.<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> The resulting structure has a calculated density of 1.587 g/cm3, in good agreement with the measured value of 1.602 g/cm3.<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> </p><p>Face-sharing creates more chance of instability, according to the third of <a href="/facts/Pauling%2527s_rules/y9hfXjhw">Pauling's rules</a>.<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a> In carnallite, the water molecules enclose the magnesium ions. This prevents the magnesium and the chloride from interacting directly; instead, the water molecules act as charge transmitters.<a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a> The five chloride anions are each coordinated to two potassium cations as well as four water molecules.<a class="footnote-ref" id="fnref:18" href="#fn:18"><sup>18</sup></a> This means that each chloride anion receives 1/6 of a +1 charge from each of the two potassium ions. The chloride also obtains 1/6 of a +1 charge from each the four water molecules. The charges thus total six 1/6 positive charges, which balance the negative charge of the chloride. These two aspects render the rare face-sharing described by the second and third of Pauling's rules acceptable in the carnallite structure.<a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a><a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a> </p> <h2 id="physical-properties">Physical properties</h2> <p>Carnallite's <a href="/facts/Refractive_index/yjkzvgeE">refractive index</a> ranges from 1.467 to 1.494.<a class="footnote-ref" id="fnref:21" href="#fn:21"><sup>21</sup></a><a class="footnote-ref" id="fnref:22" href="#fn:22"><sup>22</sup></a> Carnallite may be red as a result of <a href="/facts/Hematite/716YBzGr">hematite</a> (Fe2O3) inclusions.<a class="footnote-ref" id="fnref:23" href="#fn:23"><sup>23</sup></a> The fragmented shards of iron oxide produce red tints in the thin <a href="/facts/Lamination_(geology)/kbBpdCQM">laminae</a> of hematite.<a class="footnote-ref" id="fnref:24" href="#fn:24"><sup>24</sup></a> Carnallite is also <a href="/facts/Deliquescent/1NBGewXv">deliquescent</a> in high humidity. This implies that it is also extremely soluble in water.<a class="footnote-ref" id="fnref:25" href="#fn:25"><sup>25</sup></a> Individual crystals are pseudo-hexagonal and <a href="/facts/Tabular_habit/x2S1HVVY">tabular</a> but are extremely rarely seen.<a class="footnote-ref" id="fnref:26" href="#fn:26"><sup>26</sup></a> Field indicators of carnallite are environment of formation, absence of cleavage, and fracture. Other indicators can be density, taste, associations to local minerals, and whether it is capable of <a href="/facts/Luminescence/1QkIWyUj">luminescence</a>. Carnallite has a bitter taste.<a class="footnote-ref" id="fnref:27" href="#fn:27"><sup>27</sup></a> Carnallite may not only be <a href="/facts/Fluorescent/qsJVT2qP">fluorescent</a> but is capable of being <a href="/facts/Phosphorescent/WshJFsKV">phosphorescent</a>.<a class="footnote-ref" id="fnref:28" href="#fn:28"><sup>28</sup></a> The potassium that carnallite contains fuses easily within a flame, creating a violet color.<a class="footnote-ref" id="fnref:29" href="#fn:29"><sup>29</sup></a> </p> <h2 id="geologic-occurrence">Geologic occurrence</h2> <p>Mineral associations based on some physical properties include, but not limited to, <a href="/facts/Halite/9xEEKKT8">halite</a>, <a href="/facts/Anhydrite/66QvVbXV">anhydrite</a>, <a href="/facts/Dolomite_(mineral)/tQfyK6AF">dolomite</a>, <a href="/facts/Gypsum/MItYU70n">gypsum</a>, kainite, kieserite, polyhalite, and sylvite.<a class="footnote-ref" id="fnref:30" href="#fn:30"><sup>30</sup></a><a class="footnote-ref" id="fnref:31" href="#fn:31"><sup>31</sup></a><a class="footnote-ref" id="fnref:32" href="#fn:32"><sup>32</sup></a> </p><p>Carnallite minerals are mineral sediments known as <a href="/facts/Evaporite/vNW8fcEy">evaporites</a>. Evaporites are concentrated by evaporation of seawater. The inflow of water must be below the evaporation or use levels. This creates a prolonged evaporation period. In controlled environment experiments, the halides form when 10%–20% of the original sample of water remains.<a class="footnote-ref" id="fnref:33" href="#fn:33"><sup>33</sup></a> Closer to 10 percent sylvite followed by Carnallite form.<a class="footnote-ref" id="fnref:34" href="#fn:34"><sup>34</sup></a> </p><p>Carnallite is mostly found in saline marine deposits,<a class="footnote-ref" id="fnref:35" href="#fn:35"><sup>35</sup></a> although beds exist in the <a href="/facts/Endorheic_basin/0CHdGUlG">endorheic</a> <a href="/facts/Qaidam_Basin/QkVxMgcQ">Qaidam Basin</a> of <a href="/facts/China/lTjIXY5p">China</a>'s <a href="/facts/Qinghai_Province/g8DljGNf">Qinghai Province</a> near <a href="/facts/Dabusun_Nor_(Qinghai)/WnCa5goR">Dabusun Nor</a>.<a class="footnote-ref" id="fnref:36" href="#fn:36"><sup>36</sup></a> </p> <h2 id="uses">Uses</h2> <p>Carnallite is mostly used in fertilizers. It is an important source of <a href="/facts/Potash/4e2vBL9L">potash</a>.<a class="footnote-ref" id="fnref:37" href="#fn:37"><sup>37</sup></a> Only <a href="/facts/Sylvite/1q1ym0bQ">sylvite</a> outranks carnallite's importance in potash production.<a class="footnote-ref" id="fnref:38" href="#fn:38"><sup>38</sup></a> Both are uncommon because they are some of the last evaporites to form.<a class="footnote-ref" id="fnref:39" href="#fn:39"><sup>39</sup></a> Soluble potassium salts are the main sources for fertilizer. This is because the potassium is difficult to separate from insoluble <a href="/facts/Potassium_feldspar/qd0jwnMv">potassium feldspar</a>.<a class="footnote-ref" id="fnref:40" href="#fn:40"><sup>40</sup></a> Carnallite is a minor source of magnesium worldwide; however, it is Russia's main source.<a class="footnote-ref" id="fnref:41" href="#fn:41"><sup>41</sup></a> </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Evaporite/vNW8fcEy">Evaporite</a></li> <li><a href="/facts/List_of_minerals/4rMMcv2D">List of minerals</a></li> <li><a href="/facts/List_of_minerals_named_after_people/ElPKA5lI">List of minerals named after people</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Carnallite on Mindat <a href="http://www.mindat.org/min-906.html" target="_blank">http://www.mindat.org/min-906.html</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Carnallite on Mindat <a href="http://www.mindat.org/min-906.html" target="_blank">http://www.mindat.org/min-906.html</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Bragg, L., and G. F. Claringbull. (1965) Crystal Structure of minerals. G. Bell and Sons, Ltd., London. <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Bragg, L., and G. F. Claringbull. (1965) Crystal Structure of minerals. G. Bell and Sons, Ltd., London. <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Klein, Cornelis, B. Dutrow (2007) Manual of Mineral Science, 23rd ed.John Wiley and Sons <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Bragg, L., and G. F. Claringbull. (1965) Crystal Structure of minerals. G. Bell and Sons, Ltd., London. <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Schlemper, E. O., P. K. Gupta, and Tibor Zoltai. (1985) Refinement of the Structure of Carnallite, Mg(H2O)6KCL3. American Mineralogist 70,1309–1313. <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Schlemper, E. O., P. K. Gupta, and Tibor Zoltai. (1985) Refinement of the Structure of Carnallite, Mg(H2O)6KCL3. American Mineralogist 70,1309–1313. <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Shoval, S., S. Yariv. (1998) Formation of Carnallite Type Double Salts by Grinding Mixtures of Magnesium and Alkali Halides with the Same Anions. Journal of Thermal Analysis 51, 251–263 <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>Schlemper, E. O., P. K. Gupta, and Tibor Zoltai. (1985) Refinement of the Structure of Carnallite, Mg(H2O)6KCL3. American Mineralogist 70,1309–1313. <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>Schlemper, E. O., P. K. Gupta, and Tibor Zoltai. (1985) Refinement of the Structure of Carnallite, Mg(H2O)6KCL3. American Mineralogist 70,1309–1313. <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>Schlemper, E. O., P. K. Gupta, and Tibor Zoltai. (1985) Refinement of the Structure of Carnallite, Mg(H2O)6KCL3. American Mineralogist 70,1309–1313. <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>Schlemper, E. O., P. K. Gupta, and Tibor Zoltai. (1985) Refinement of the Structure of Carnallite, Mg(H2O)6KCL3. American Mineralogist 70,1309–1313. <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>Schlemper, E. O., P. K. Gupta, and Tibor Zoltai. (1985) Refinement of the Structure of Carnallite, Mg(H2O)6KCL3. American Mineralogist 70,1309–1313. <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> <li id="fn:15"><p>Schlemper, E. O., P. K. Gupta, and Tibor Zoltai. (1985) Refinement of the Structure of Carnallite, Mg(H2O)6KCL3. American Mineralogist 70,1309–1313. <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li> <li id="fn:16"><p>Klein, Cornelis, B. Dutrow (2007) Manual of Mineral Science, 23rd ed.John Wiley and Sons <a href="#fnref:16" class="footnote-back-ref">↩</a></p></li> <li id="fn:17"><p>Schlemper, E. O., P. K. Gupta, and Tibor Zoltai. (1985) Refinement of the Structure of Carnallite, Mg(H2O)6KCL3. American Mineralogist 70,1309–1313. <a href="#fnref:17" class="footnote-back-ref">↩</a></p></li> <li id="fn:18"><p>Schlemper, E. O., P. K. Gupta, and Tibor Zoltai. (1985) Refinement of the Structure of Carnallite, Mg(H2O)6KCL3. American Mineralogist 70,1309–1313. <a href="#fnref:18" class="footnote-back-ref">↩</a></p></li> <li id="fn:19"><p>Klein, Cornelis, B. Dutrow (2007) Manual of Mineral Science, 23rd ed.John Wiley and Sons <a href="#fnref:19" class="footnote-back-ref">↩</a></p></li> <li id="fn:20"><p>Schlemper, E. O., P. K. Gupta, and Tibor Zoltai. (1985) Refinement of the Structure of Carnallite, Mg(H2O)6KCL3. American Mineralogist 70,1309–1313. <a href="#fnref:20" class="footnote-back-ref">↩</a></p></li> <li id="fn:21"><p>Klein, Cornelis, B. Dutrow (2007) Manual of Mineral Science, 23rd ed.John Wiley and Sons <a href="#fnref:21" class="footnote-back-ref">↩</a></p></li> <li id="fn:22"><p>Mottana, Annibale, R. Crespi, and G. Liborio. (1978) Rocks and Minerals. Simon and Schuster. NY. <a href="#fnref:22" class="footnote-back-ref">↩</a></p></li> <li id="fn:23"><p>Mottana, Annibale, R. Crespi, and G. Liborio. (1978) Rocks and Minerals. Simon and Schuster. NY. <a href="#fnref:23" class="footnote-back-ref">↩</a></p></li> <li id="fn:24"><p>Mottana, Annibale, R. Crespi, and G. Liborio. (1978) Rocks and Minerals. Simon and Schuster. NY. <a href="#fnref:24" class="footnote-back-ref">↩</a></p></li> <li id="fn:25"><p>Mottana, Annibale, R. Crespi, and G. Liborio. (1978) Rocks and Minerals. Simon and Schuster. NY. <a href="#fnref:25" class="footnote-back-ref">↩</a></p></li> <li id="fn:26"><p>Blatt, H. (1992) Sedimentary Petrology, 2nd ed. W.H. Freeman and Co., San Francisco. <a href="#fnref:26" class="footnote-back-ref">↩</a></p></li> <li id="fn:27"><p>Blatt, H. (1992) Sedimentary Petrology, 2nd ed. W.H. Freeman and Co., San Francisco. <a href="#fnref:27" class="footnote-back-ref">↩</a></p></li> <li id="fn:28"><p>Blatt, H. (1992) Sedimentary Petrology, 2nd ed. W.H. Freeman and Co., San Francisco. <a href="#fnref:28" class="footnote-back-ref">↩</a></p></li> <li id="fn:29"><p>Blatt, H. (1992) Sedimentary Petrology, 2nd ed. W.H. Freeman and Co., San Francisco. <a href="#fnref:29" class="footnote-back-ref">↩</a></p></li> <li id="fn:30"><p>Klein, Cornelis, B. Dutrow (2007) Manual of Mineral Science, 23rd ed.John Wiley and Sons <a href="#fnref:30" class="footnote-back-ref">↩</a></p></li> <li id="fn:31"><p>Anthony, J. W., R. A. Bideaux, R. A., Bladh, K. W. and M. C. Nichols. (1997) Handbook of Mineralogy. Vol. 3 Halides, hydroxides, oxides. Mineral Data Publications, Tucson, Arizona. <a href="#fnref:31" class="footnote-back-ref">↩</a></p></li> <li id="fn:32"><p>Phosphate, potash, and sulfur- A special issue. (1979) Economic Geology 74, 191–493. <a href="#fnref:32" class="footnote-back-ref">↩</a></p></li> <li id="fn:33"><p>Smetannikov, A. F., (2010) Hydrogen Generation during the Radiolysis of Crystallization water in Carnallite and Possible Consequences of this Process Geochemistry International 49, 971–980 <a href="#fnref:33" class="footnote-back-ref">↩</a></p></li> <li id="fn:34"><p>Smetannikov, A. F., (2010) Hydrogen Generation during the Radiolysis of Crystallization water in Carnallite and Possible Consequences of this Process Geochemistry International 49, 971–980 <a href="#fnref:34" class="footnote-back-ref">↩</a></p></li> <li id="fn:35"><p>Blatt, H. (1992) Sedimentary Petrology, 2nd ed. W.H. Freeman and Co., San Francisco. <a href="#fnref:35" class="footnote-back-ref">↩</a></p></li> <li id="fn:36"><p>Garrett, Donald Everett (1996), Potash: Deposits, Processing, Properties, and Uses, London: Chapman & Hall, p. 177, ISBN 9789400915459. <a href="9789400915459" target="_blank">9789400915459</a> <a href="#fnref:36" class="footnote-back-ref">↩</a></p></li> <li id="fn:37"><p>Phosphate, potash, and sulfur- A special issue. (1979) Economic Geology 74, 191–493. <a href="#fnref:37" class="footnote-back-ref">↩</a></p></li> <li id="fn:38"><p>Phosphate, potash, and sulfur- A special issue. (1979) Economic Geology 74, 191–493. <a href="#fnref:38" class="footnote-back-ref">↩</a></p></li> <li id="fn:39"><p>Phosphate, potash, and sulfur- A special issue. (1979) Economic Geology 74, 191–493. <a href="#fnref:39" class="footnote-back-ref">↩</a></p></li> <li id="fn:40"><p>Phosphate, potash, and sulfur- A special issue. (1979) Economic Geology 74, 191–493. <a href="#fnref:40" class="footnote-back-ref">↩</a></p></li> <li id="fn:41"><p>Phosphate, potash, and sulfur- A special issue. (1979) Economic Geology 74, 191–493. <a href="#fnref:41" class="footnote-back-ref">↩</a></p></li> </ol>