NaCl is cubic and crystallizes, from its solution in water, in form of cubes {100}. The crystal form can depend on additives, and if the water contains urea, one obtaines octahedra {111}. I'm almost sure that many years ago I read that rhombododecahedra {110} can also be obtained.
Can anybody help me to find the conditions under which {110} crystals are obtained? Or am I wrong?
This is a nice classic one. I searched for the answer in Johann Samuel Traugott Gehler's "Physikalisches Wörterbuch", which was first published in 1787. The edition in the Google electronic library is from 1830. According to this book, adding urea gives octahedra of sodium chloride, while adding boric acid results in cuboctrahedra. Unfortunately, nothing about {110}.
As I have it already open: The other popular compound for crystallization experiments, alum, normally takes octahedral shape. Adding "alkali" (potassium carbonate or sodium carbonate) leads to cubic crystals, with hydrocloric acid one gets cubo-icosahedra, and addition of boric acid is supposed to result in cubo-octo-dodecahedra.
As for NaCl rhombododecahedra: I found a patent claiming that adding glycine to a glycine concentration ranging between 10 and 25% to the saturated salt solution will do the trick.
This is a nice classic one. I searched for the answer in Johann Samuel Traugott Gehler's "Physikalisches Wörterbuch", which was first published in 1787. The edition in the Google electronic library is from 1830. According to this book, adding urea gives octahedra of sodium chloride, while adding boric acid results in cuboctrahedra. Unfortunately, nothing about {110}.
As I have it already open: The other popular compound for crystallization experiments, alum, normally takes octahedral shape. Adding "alkali" (potassium carbonate or sodium carbonate) leads to cubic crystals, with hydrocloric acid one gets cubo-icosahedra, and addition of boric acid is supposed to result in cubo-octo-dodecahedra.
As for NaCl rhombododecahedra: I found a patent claiming that adding glycine to a glycine concentration ranging between 10 and 25% to the saturated salt solution will do the trick.
Dear Miguel,
there is a long debate about the morphology change of NaCl growing from aqueous solution in the presence of additives. Concerning the {110} form, the best finding (and interpretation) has been given by the Kern's group in Marseille 50 years. You will find enclosed some papers concerning your nice question, even if they are mainly devoted to the appearance of the octahedron.
My research group is working on the interpretation of {110} appearance in the presence of glycine.
This is a complex subject (which involves all the alkali halides).
All the best
Dino
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