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Thread: Salt crystal hardness

  1. #1 Salt crystal hardness 
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    How hard are salt crystals, like the ones you see a lot of instructions for making with a string in warm salty water? Will they break up fairly easily? Or really hard that you could actually make things out of them ?


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    Forum Freshman Brett's Avatar
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    Quote Originally Posted by Sonar87 View Post
    How hard are salt crystals, like the ones you see a lot of instructions for making with a string in warm salty water? Will they break up fairly easily? Or really hard that you could actually make things out of them ?
    It would take a very long time to build anything out of them. rather use something else?


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    Well, I'm not actually planning on doing it, I know it would take a lot. I was just curious.
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    Quote Originally Posted by Sonar87 View Post
    How hard are salt crystals, like the ones you see a lot of instructions for making with a string in warm salty water? Will they break up fairly easily? Or really hard that you could actually make things out of them ?
    According to Wiki, the Moh hardness of halite (the mineral name given to NaCl found in rocks) is 2-2.5. That means it is quite soft, as minerals go.

    Halite - Wikipedia, the free encyclopedia

    Suggest researching Moh and other hardness scales if you need to put this into context.

    Please note hardness is a measure of resistance to scratching (and ability to scratch other things). It may not necessarily be a good guide to mechanical strength (compressive or tensile), which is what is most relevant for use as a building material.
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    Cool, thanks.
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    Forum Radioactive Isotope Paleoichneum's Avatar
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    really what you also need to look at on this is the cleavage of the mineral. Halite cleaves very easily on three planes so anything constructed from it will be very prone to scratching and breaking. (not to mention dissolving in humidity)
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  8. #7  
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    Quote Originally Posted by Brett View Post
    Quote Originally Posted by Sonar87 View Post
    How hard are salt crystals, like the ones you see a lot of instructions for making with a string in warm salty water? Will they break up fairly easily? Or really hard that you could actually make things out of them ?
    It would take a very long time to build anything out of them. rather use something else?
    Discs made of sodium chloride are used in infrared spectroscopy (due to the transparency of sodium chloride to infrared radiation).
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    Salt can have surprising mechanical strength when it crystallises in large masses. I once did an investigation at a solar salt production facility where they were having problems digging the stuff up from their evaporation ponds. They were actually breaking the ripper tynes on the back of a grader. As I recall, there were small amounts of manganese in the incoming brine and that had a significant effect on the mechanical strength of the crystallised salt. The manganese needed to be precipitated out before crystallisation to reduce the strength of the salt so that is could be broken up and harvested.

    I have no doubt that you could build structures from blocks of the salt cut from those evaporation ponds. Typical facet sizes on the exposed crystal faces were about 1cm across and the crystals were densely inter-grown to a depth of perhaps 400 mm. I have even thought that you could build a pyramid by evaporating successive layers within a movable system of bunds.

    The effect of humidity on salt is due largely to the magnesium chloride content. Pure or 'vacuum' salt is stable up to a rh of 75%. Though large masses of salt crystal do suffer some surface damage due to cycling of humidity, it a relatively minor effect. I have had specimens lying around for years with no degradation.
    Last edited by Warron; January 19th, 2014 at 10:52 PM.
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