Halite: Difference between revisions

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<bibimport />
Authors: [[User:Hschwarz|Hans-Jürgen Schwarz]], [[user:NMainusch|Nils Mainusch]]
Authors: [[User:Hschwarz|Hans-Jürgen Schwarz]], Nils Mainusch
<br>English version by [[user:CGerdwilker|Christa Gerdwilker]]
<br>English version by Christa Gerdwilker  
<br>back to [[Chloride]]  
<br>back to [[Chloride]]  




{{Infobox_Salt
{{Infobox_Salt
|Footnote=<ref>http://webmineral.com/data/Halite.shtml accessed 28.07.2010</ref><ref>http://www.mindat.org/min-1804.html accessed 28.07.2010</ref><ref>http://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Halit accessed 28.07.2010</ref>
|Footnote=<ref>http://webmineral.com/data/Halite.shtml accessed 28.07.2010</ref><ref>http://www.mindat.org/min-1804.html accessed 28.07.2010</ref><ref>http://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Halit accessed 28.07.2010</ref> <ref name=hydrohalit>http://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Hydrohalit accessed 28.07.2010</ref>
|photo                =  [[Image:NaCl 27.4.2006-10x.JPG|300px]]
|photo                =  [[Image:NaCl 27.4.2006-10x.JPG|300px]]
|mineralogical_Name  = Halite
|mineralogical_Name  = Halite
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|Trivial_Name        = Common Salt, Rock Salt
|Trivial_Name        = Common Salt, Rock Salt
|chemical_Formula      = NaCl
|chemical_Formula      = NaCl
|Hydratforms=Sodiumchloride Dihydrate/Hydrohalite (NaCl•2H<sub>2</sub>O)<ref name=hydrohalit>http://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Hydrohalit gelesen 28.07.2010</ref>
|Hydratforms=NaCl•2H<sub>2</sub>O ([[Hydrohalite]])
|Crystal_System      =cubic
|Crystal_System      =cubic
|Crystal_Structure  =
|Crystal_Structure  =
|Deliqueszenzhumidity =75.7% (10°C), 75.3% (25°C)
|Deliqueszenzhumidity =75.4%  
|Solubility          = 358 g/l
|Solubility          = 6.135 mol/kg
|Density              =2.163 g/cm<sup>3</sup>
|Density              =2.163 g/cm<sup>3</sup>
|MolVolume            =27.02 cm<sup>3</sup>/mol
|MolVolume            =27.02 cm<sup>3</sup>/mol
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|Crystal_Habit        =cubic crystal, granular, massive aggregates
|Crystal_Habit        =cubic crystal, granular, massive aggregates
|Twinning            =none
|Twinning            =none
|Refractive_Indices  =n=1.544
|Refractive_Indices  =n<sub>D</sub>=1.5443
|Birefringence        =
|Birefringence        =
|optical_Orientation  =isotropic
|optical_Orientation  =isotropic
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|Phase_Transition    =
|Phase_Transition    =
|chemBehavior        =
|chemBehavior        =
|Comments            =slightly watersoluble
|Comments            = water soluble
|Literature          =<bib id="Steiger.etal:2014"/> <bib id="Robie.etal:1978"/> <bib id="Dana:1951"/>
}}  
}}  
== Abstract  ==
== Abstract  ==


== Halite origins ==
== Occurrence ==


Sodium chloride is obtained through mining or derived from the sea or salt lakes and is commonly used for cooking or as road gritting salt. <br>
Sodium chloride is obtained through mining or derived from the sea or salt lakes and is commonly used for cooking or as deicing salt for roads. <br>
The salt content of sea water is approx. 2,7 M.%.<br>
The sodium chloride content of sea water is around 2.7 M.%.<br>


== Causes of halite formation on monuments ==
== Origin of the halite found on monuments ==


Contact with materials containing soluble sodium-based ingredients can result in the efflorescence of sodium chloride on monuments. A primary example is the high sodium content of cements. Contamination with sodium and chloride ions can also occur through contact with salt laden ground or surface water. A range of cleaning materials (e.g. acidic and caustic cleaners) and especially previously used restoration materials (e.g. water glass) can introduce sodium and chloride ions into monuments. Further common sources of halite are rock salt used in road gritting which predominantly consists of sodium chloride, as well as salt laden seawater in coastal areas.<br>
Sodium chloride can enter buildings or monuments when these are in contact with materials containing this salt or even other salts containing either sodium or chloride, that might combine to produce NaCl in or efflorescence on them. Contamination with sodium and chloride ions can also occur through contact with salt laden ground or surface water. A range of cleaning materials (e.g., acidic and alkaline cleaners or combination of them), or previously used restoration materials (e.g., water glass) as well as Portland cement, can introduce sodium and chloride ions into monuments. Further common and important sources are deicing salts and maritime environments where the air and fogs may contain a significant amount of sodium chloride in suspension or dissolved in droplets.<br>


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== Solubility behavior ==
== Solubility behavior ==


The commonly occurring halite found in northern Germany has a solubility of 358 g/l (20°C) and thus belongs to the group of very soluble and, therefore, easily mobilized salts. Its solubility changes comparatively little within a temperature range of  10 -30°C.  
The commonly occurring halite has a solubility of 6.13 mol/kg (20°C) and can be considered as a very soluble and, therefore, easily mobilized salt. Its solubility changes not significantly within a temperature range of  10 -30°C.  


[[Image:NaCl s.jpg|thumb|right|400px|Figure1:Phase diagram of halite. Graphic: Michael Steiger]]  
[[Image:S NaCl.jpg|thumb|left|800px|Figure 1: Solubility of sodium chloride in water. The molality ''m'' [n(NaCl)•kg(H<sub>2</sub>O)<sup>-1</sup>] is plotted versus the temperature.]]  


<br clear="all">  
<br clear="all">  
{|border="2" cellspacing="0" cellpadding="4" width="52%" align="left" class="wikitable"
{|border="2" cellspacing="0" cellpadding="4" width="52%" align="left" class="wikitable"
|+''Table 1: Solubility of halite in relation to temperature [according to <bib id="Stark.etal:1996" /> and <bib id="DAns:1933" /> ''                     
|+''Table 1: Solubility of halite at different round temperatures [according to <bib id="Steiger.etal:2008c"/>.''                     
|-
|-
|bgcolor = "#F0F0F0"| '''Temperature'''  
|bgcolor = "#F0F0F0"| '''Temperature'''  
|bgcolor = "#F0F0F0" align=center| '''10°C'''  
|bgcolor = "#F0F0F0" align=center| '''10°C'''  
|bgcolor = "#F0F0F0" align=center| '''20°C'''  
|bgcolor = "#F0F0F0" align=center| '''20°C'''  
|bgcolor = "#F0F0F0" align=center| '''30°C'''
|bgcolor = "#F0F0F0" align=center| '''40°C'''
|bgcolor = "#F0F0F0" align=center| '''40°C'''
|-
|-
|bgcolor = "#F7F7F7" | Solubility [g/l]  
|bgcolor = "#F7F7F7" | Solubility [mol/kg]  
|bgcolor = "#FFFFEO" align=center| 356,5
|bgcolor = "#FFFFEO" align=center| 6.11
|bgcolor = "#FFFFEO" align=center| 358,8
|bgcolor = "#FFFFEO" align=center| 6.13
|bgcolor = "#FFFFEO" align=center| 364,2
|bgcolor = "#FFFFEO" align=center| 6.17
|bgcolor = "#FFFFEO" align=center| 6.22
|}
|}
<br clear=all>
<br clear=all>


== Hygroscopicity  ==
== Hygroscopicity  ==
Halite has a deliquescence humidity of about 75% RH, therefore it tends to pick up moisture easily in most temperate climates.
[[Image:D NaCl e.jpg|thumb|left|800px|Figure 2: Deliquescence behaviour of sodium chloride. The water activity ''a<sub>w</sub>'' is plotted versus the temperature.]]
<!--Temperature variations hardly affect the deliquescence point of halite which is illustrated below in comparison with potassium nitrate and natrite.-->
<br clear=all>
{|border="2" cellspacing="0" cellpadding="4" width="52%" align="left" class="wikitable"
|+''Table 2: Deliquescence humidities of sodium chloride at different round temperatures <bib id="Steiger etal: 2014"/>''                   
|-
|bgcolor = "#F0F0F0" align=center| 0°C
|bgcolor = "#F0F0F0" align=center| 10°C
|bgcolor = "#F0F0F0" align=center| 20°C
|bgcolor = "#F0F0F0" align=center| 30°C
|bgcolor = "#F0F0F0" align=center| 40°C
|bgcolor = "#F0F0F0" align=center| 50°C
|-
|bgcolor = "#FFFFEO" align=center| 75.9%r.h.
|bgcolor = "#FFFFEO" align=center| 75.6%r.h.
|bgcolor = "#FFFFEO" align=center| 75.4%r.h.
|bgcolor = "#FFFFEO" align=center| 75.2%r.h.
|bgcolor = "#FFFFEO" align=center| 75.2%r.h.
|bgcolor = "#FFFFEO" align=center| 74.8%r.h.
|}
<br clear=all>


[[Image:NaCl a.jpg|thumb|right|400px|Figure 2: The system NaCl/H<sub>2</sub>O within temperature range of  -20°C to 80°C. Graphic: Michael Steiger]]


Halite’s deliquescence humidity of approx. 75% is often crossed in the climate of northern Europe. <!--Temperature variations hardly affect the deliquescence point of halite which is illustrated below in comparison with potassium nitrate and natrite.
-->




<br> '''Moisture sorption:'''<br>Theoretically 1g NaCl can absorb 4,3g moisture. The moisture sorption during varying relative humidity levels is:   
<br> '''Moisture sorption:'''<br>Theoretically 1g NaCl can take up 4.3g of moisture, i.e., water vapor. The moisture sorption during varying relative humidity levels is:   


<br clear="all">  
<br clear="all">  
{|border="2" cellspacing="0" cellpadding="4" width="52%" align="left" class="wikitable sortable"
{|border="2" cellspacing="0" cellpadding="4" width="52%" align="left" class="wikitable sortable"
|+''Tabelle 2:Moisture sorption in M% after 56 days according to <bib id=Vogt.etal:1993/> ''                   
|+''Table 3:Moisture sorption in M% after 56 days according to <bib id=''Vogt.etal:1993''/>                    
|-
|-
|bgcolor = "#F0F0F0"| '''Relative humidity during storge/salt phase'''
|bgcolor = "#F0F0F0" align=center| '''Relative humidity during storge/salt phase'''
|bgcolor = "#F0F0F0" align=center| '''NaCl'''  
|bgcolor = "#F0F0F0" align=center| '''NaCl'''  
|-
|-
|bgcolor = "#F7F7F7" | '''87% RH'''
|bgcolor = "#F7F7F7" align=center| '''87% RH'''
|bgcolor = "#FFFFEO" align=center| 153
|bgcolor = "#FFFFEO" align=center| 153
|-
|-
|bgcolor = "#F7F7F7" | '''81% RH'''
|bgcolor = "#F7F7F7" align=center| '''81% RH'''
|bgcolor = "#FFFFEO" align=center| 22
|bgcolor = "#FFFFEO" align=center| 22
|-
|-
|bgcolor = "#F7F7F7" | '''79% RH'''
|bgcolor = "#F7F7F7" align=center| '''79% RH'''
|bgcolor = "#FFFFEO" align=center| 7
|bgcolor = "#FFFFEO" align=center| 7
|}
|}
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<br clear=all>


<!--
== Crystallization pressure  ==
== Crystallization pressure  ==


The crystallization of halite from a water-based solution results in a crystallization pressure of 55,4-65,4 N/mm<sup>2</sup> <bib id="Winkler:1975" /> (for comparison, the crystallization pressure of different salts can range from 7,2-65,4 N/mm<sup>2</sup>). These values need to be considered in conjunction with temperature and concentration and can, therefore, only act as indicators of damage potential in relation to salt crystallization pressure. In comparison to other salts, the crystallization pressure of halite is extremely high.  
The crystallization of halite from an aqueous solution results in a crystallization pressure of 55,4-65,4 N/mm<sup>2</sup> <bib id="Winkler:1975" /> (for comparison, the crystallization pressure of different salts can range from 7,2-65,4 N/mm<sup>2</sup>). These values need to be considered in conjunction with temperature and concentration and can, therefore, only act as indicators of damage potential in relation to salt crystallization pressure. In comparison to other salts, the crystallization pressure of halite is extremely high.
-->


== Hydration behavior  ==
== Hydration behavior  ==


Under normal conditions only the unhydrated form of halite exists. Only at a temperature of below 0.15 °C does a saturated water-based sodium chloride solution result in the precipitation of a deposit of dihydrate hydrohalite<ref name=hydrohalit>http://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Hydrohalit accessed 28.07.2010</ref>.
Under normal environmental conditions only halite will crystallize out of a saturated solution. The hydrated form, dihydrate hydrohalite<ref name=hydrohalit>http://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Hydrohalit accessed 28.07.2010</ref> will only precipitate out at temperatures below 0.15°C.


<!--
<!--
=== Hydration pressure  ===
=== Hydration pressure  ===


=== Transformation reactions  ===
=== Transition reactions  ===


== <br>Analytical validation  ==
== <br>Analytical validation  ==
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== Microscopy ==
== Microscopy ==


===  Laboratory examinations ===
===  Laboratory analysis ===
   
   
Sodium chloride crystals can be reliably identified on the basis of morphological features. Individual particles usually form cubic or octahedral shapes and, therefore, clearly display right angles in their crystal construction. <br>  
Sodium chloride crystals can be reliably identified on the basis of their morphological features. Individual particles usually form cubic or octahedral shapes and, therefore, clearly display right angles in their crystal construction. <br>  


'''Refractive index:'''&nbsp; n<sub>D</sub> = 1,544<br>'''Crystal category:'''&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; cubic<br>  
'''Refractive index:'''&nbsp; n<sub>D</sub> = 1.544<br>'''Crystal category:'''&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; cubic<br>  


'''Examinations under the polarizing microscope:'''  
'''Examination by polarized microscopy:'''  


Together with potassium chloride, sodium chloride is one of the few salts belonging to the cubic crystal system which cause damage to masonry. Because of its isotropic internal structure it does not display birefringence.   
There are few salts belonging to the cubic crystal system which can be found in masonry, i.e., sodium chloride (halite), potassium chloride (sylvite) and calcium fluoride (flourite). Only the two first salts are highly soluble and therefore they are the ones that can cause damage to the masonry. Because of its isotropic internal structure these salts do not display birefringence.   


The classification of the refractive index occurs by immersion method in a standard oil with a refractive index of n<sub>D</sub> =1,518. Halite crystals display the same optical density in every direction so that the speed and orientation of linear polarized light waves are not distorted. When viewed between crossed polars, the crystals are not visible but appear (independent of orientation) extinguished.   
The refractive index can be measured with the immersion method by using a standard oil with a refractive index of n<sub>D</sub> =1.518. Halite crystals display the same optical density in every direction so that the speed and orientation of linear polarized light waves are not distorted, therefore, when viewed between crossed polars, the crystals are not visible, i.e., they show "extinction".   


<br> '''Differentiating of halite from similar salts:'''<br>  
<br> '''Differentiation of halite from similar salts:'''<br>  


The group of isotropic salts causing masonry damage consists of halite, sylvine and fluorite. All these phases can be differenciated easily.  
The three above mentioned isotropic salts can be easily differentiated.


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{|border="2" cellspacing="0" cellpadding="4" width="50%" align="left" class="wikitable"
{|border="2" cellspacing="0" cellpadding="4" width="50%" align="left" class="wikitable"
|+''Table 3: Identification features of other chlorides''                     
|+''Table 4: Identification features of other chlorides''                     
|-
|-
{| cellspacing="1" cellpadding="1" border="1" style="width: 498px; height: 85px;"
{| cellspacing="1" cellpadding="1" border="1" style="width: 498px; height: 85px;"
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|-
|-
|bgcolor = "#F7F7F7"| [[Sylvine]] KCl  
|bgcolor = "#F7F7F7"| [[Sylvine]] KCl  
|bgcolor = "#FFFFEO"| Refractive index under 1,518.
|bgcolor = "#FFFFEO"| Refractive index below 1,518.
|-
|-
|bgcolor = "#F7F7F7"| [[Fluorite]] CaF<sub>2</sub>  
|bgcolor = "#F7F7F7"| [[Fluorite]] CaF<sub>2</sub>  
|bgcolor = "#FFFFEO"| Refractive index under 1,518, barely water soluble.
|bgcolor = "#FFFFEO"| Refractive index below 1,518, barely water soluble.
|}
|}


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=== Under the polarizing microscope ===
=== Under the polarizing microscope ===


<gallery caption="Precipitate from watery sample on microscope slide" widths="200px" heights="150px" perrow="3">
<gallery caption="Precipitated from the evaporation of an aqueous solution of the sample on microscope slides" widths="200px" heights="150px" perrow="3">


Image:NaCl 27.4.2006-10x (1).JPG|Sodium chloride, precipitate from watery sample on microscope slide  
Image:NaCl 27.4.2006-10x (1).JPG|Sodium chloride, precipitate from an aqueous solution on microscope slide  
Image:NaCl 27.4.2006-10x (2).JPG|Sodium chloride, precipitate from watery sample on microscope slide  
Image:NaCl 27.4.2006-10x (2).JPG|Sodium chloride, precipitate from an aqueous solution on microscope slide  
Image:NaCl 27.4.2006-10x (5).JPG|Sodium chloride, precipitate from watery sample on microscope slide  
Image:NaCl 27.4.2006-10x (5).JPG|Sodium chloride, precipitate from an aqueous solution on microscope slide  
Image:NaCl 27.4.2006-10x (6).JPG|Sodium chloride, precipitate from watery sample on microscope slide  
Image:NaCl 27.4.2006-10x (6).JPG|Sodium chloride, precipitate from an aqueous solution on microscope slide  
Image:NaCl 27.4.2006-10x.JPG| Sodium chloride, precipitate from watery sample on microscope slide  
Image:NaCl 27.4.2006-10x.JPG| Sodium chloride, precipitate from an aqueous solution on microscope slide  
Image:NaCl+CaSO4 reale Probe 01.JPG|Sodium chloride and calcium sulphate in real sample, precipitate from watery solution on microscopic slide
Image:NaCl+CaSO4 reale Probe 01.JPG|Sodium chloride and calcium sulphate in real sample, precipitate from an aqueous solution on microscopic slide
Image:NaCl+CaSO4 reale Probe 02.JPG|Sodium chloride and calcium sulphate in real sample, precipitate from watery solution on microscopic slide
Image:NaCl+CaSO4 reale Probe 02.JPG|Sodium chloride and calcium sulphate in real sample, precipitate from an aqueous solution on microscopic slide


</gallery>  
</gallery>  


<!--
=== Through the Scanning Electron Microscope  ===


-->
=== Scanning Electron Microscope photomicrographs  ===
 
<gallery caption="" widths="200px" heights="150px" perrow="2">
 
Image:NaCl S.Stefano.jpg|NaCl whisker growing on brick from a church in Venice. The sample had been kept in a film cartridge so it dried out very slowly. A nice cubic crystal can be seen at the tip of the whisker that had been on the surface of the brick as efflorescence when the sample was taken.   
</gallery>


== Weblinks  ==
== Weblinks  ==
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<!-- System NaCl-H2O was by BRAITSCH (1962) and FRENZEL (1980) -->
<!-- System NaCl-H2O was by BRAITSCH (1962) and FRENZEL (1980) -->


<bibprint />  
<biblist/>  


[[Category:Halite]] [[Category:Hschwarz]] [[Category:R-MSteiger]] [[Category:inProgress]] [[Category:Chloride]] [[Category:Salt]]
'''More Literature'''
<!--
<bibprint filter="title:%NaCl%"/>
-->
[[Category:Halite]] [[Category:Schwarz,Hans-Jürgen]][[Category:Mainusch,Nils]] [[Category:R-MSteiger]] [[Category:Chloride]] [[Category:Salt]][[Category:approved]][[Category:List]]

Latest revision as of 10:24, 29 August 2023

Authors: Hans-Jürgen Schwarz, Nils Mainusch
English version by Christa Gerdwilker
back to Chloride


Halite[1][2][3] [4]
NaCl 27.4.2006-10x.JPG
Mineralogical name Halite
Chemical name Sodium chloride
Trivial name Common Salt, Rock Salt
Chemical formula NaCl
Other forms NaCl•2H2O (Hydrohalite)
Crystal system cubic
Crystal structure
Deliquescence humidity 20°C 75.4%
Solubility (g/l) at 20°C 6.135 mol/kg
Density (g/cm³) 2.163 g/cm3
Molar volume 27.02 cm3/mol
Molar weight 58.44 g/mol
Transparency transparent to translucent
Cleavage perfect
Crystal habit cubic crystal, granular, massive aggregates
Twinning none
Phase transition
Chemical behavior
Comments water soluble
Crystal Optics
Refractive Indices nD=1.5443
Birefringence
Optical Orientation isotropic
Pleochroism
Dispersion
Used Literature
[Steiger.etal:2014]Title: Weathering and Deterioration
Author: Steiger, Michael; Charola A. Elena; Sterflinger, Katja
Link to Google Scholar
[Robie.etal:1978]Title: Thermodynamic properties of minerals and related substances at 298.15 K and 1 bar pressure and higher temperatures
Author: Robie R.A., Hemingway B.S.; Fisher J.A.
Link to Google Scholar
[Dana:1951]Title: Dana's System of Mineralogy
Author: Dana J.D.
Link to Google Scholar


Abstract[edit]

Occurrence[edit]

Sodium chloride is obtained through mining or derived from the sea or salt lakes and is commonly used for cooking or as deicing salt for roads.
The sodium chloride content of sea water is around 2.7 M.%.

Origin of the halite found on monuments[edit]

Sodium chloride can enter buildings or monuments when these are in contact with materials containing this salt or even other salts containing either sodium or chloride, that might combine to produce NaCl in or efflorescence on them. Contamination with sodium and chloride ions can also occur through contact with salt laden ground or surface water. A range of cleaning materials (e.g., acidic and alkaline cleaners or combination of them), or previously used restoration materials (e.g., water glass) as well as Portland cement, can introduce sodium and chloride ions into monuments. Further common and important sources are deicing salts and maritime environments where the air and fogs may contain a significant amount of sodium chloride in suspension or dissolved in droplets.


Solubility behavior[edit]

The commonly occurring halite has a solubility of 6.13 mol/kg (20°C) and can be considered as a very soluble and, therefore, easily mobilized salt. Its solubility changes not significantly within a temperature range of 10 -30°C.

Figure 1: Solubility of sodium chloride in water. The molality m [n(NaCl)•kg(H2O)-1] is plotted versus the temperature.


Table 1: Solubility of halite at different round temperatures [according to [Steiger.etal:2008c]Title: An improved model incorporating Pitzer’s equations for calculation of thermodynamic properties of pore solutions implemented into an efficient program code
Author: Steiger, Michael; Kiekbusch, Jana; Nicolai, Andreas
Link to Google Scholar
.
Temperature 10°C 20°C 30°C 40°C
Solubility [mol/kg] 6.11 6.13 6.17 6.22


Hygroscopicity[edit]

Halite has a deliquescence humidity of about 75% RH, therefore it tends to pick up moisture easily in most temperate climates.

Figure 2: Deliquescence behaviour of sodium chloride. The water activity aw is plotted versus the temperature.


Table 2: Deliquescence humidities of sodium chloride at different round temperatures [Steiger etal: 2014]Title: Weathering and Deterioration
Author: Steiger, Michael; Charola A. Elena; Sterflinger, Katja
Link to Google Scholar
0°C 10°C 20°C 30°C 40°C 50°C
75.9%r.h. 75.6%r.h. 75.4%r.h. 75.2%r.h. 75.2%r.h. 74.8%r.h.





Moisture sorption:
Theoretically 1g NaCl can take up 4.3g of moisture, i.e., water vapor. The moisture sorption during varying relative humidity levels is:


Table 3:Moisture sorption in M% after 56 days according to []The entry doesn't exist yet.
Relative humidity during storge/salt phase NaCl
87% RH 153
81% RH 22
79% RH 7



Hydration behavior[edit]

Under normal environmental conditions only halite will crystallize out of a saturated solution. The hydrated form, dihydrate hydrohalite[4] will only precipitate out at temperatures below 0.15°C.


Microscopy[edit]

Laboratory analysis[edit]

Sodium chloride crystals can be reliably identified on the basis of their morphological features. Individual particles usually form cubic or octahedral shapes and, therefore, clearly display right angles in their crystal construction.

Refractive index:  nD = 1.544
Crystal category:       cubic

Examination by polarized microscopy:

There are few salts belonging to the cubic crystal system which can be found in masonry, i.e., sodium chloride (halite), potassium chloride (sylvite) and calcium fluoride (flourite). Only the two first salts are highly soluble and therefore they are the ones that can cause damage to the masonry. Because of its isotropic internal structure these salts do not display birefringence.

The refractive index can be measured with the immersion method by using a standard oil with a refractive index of nD =1.518. Halite crystals display the same optical density in every direction so that the speed and orientation of linear polarized light waves are not distorted, therefore, when viewed between crossed polars, the crystals are not visible, i.e., they show "extinction".


Differentiation of halite from similar salts:

The three above mentioned isotropic salts can be easily differentiated.


Table 4: Identification features of other chlorides
Salt phase Identification features
Sylvine KCl Refractive index below 1,518.
Fluorite CaF2 Refractive index below 1,518, barely water soluble.


Images of salts and salt damage[edit]

In situ[edit]

Under the polarizing microscope[edit]


Scanning Electron Microscope photomicrographs[edit]

Weblinks[edit]

Literature[edit]

[Dana:1951]Dana E.S. (eds.) Dana J.D. (1951): Dana's System of Mineralogy, 7, Wiley & SonsLink to Google Scholar
[Robie.etal:1978]Robie R.A., Hemingway B.S.; Fisher J.A. (1978): Thermodynamic properties of minerals and related substances at 298.15 K and 1 bar pressure and higher temperatures. In: U.S. Geol. Surv. Bull, 1452 ()Link to Google Scholar
[Steiger]The entry doesn't exist yet.
[Steiger.etal:2008c]Steiger, Michael; Kiekbusch, Jana; Nicolai, Andreas (2008): An improved model incorporating Pitzer’s equations for calculation of thermodynamic properties of pore solutions implemented into an efficient program code. In: Construction and Building Materials, 22 (8), 1841-1850, 10.1016/j.conbuildmat.2007.04.020Link to Google Scholar
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