Mirabilite: Difference between revisions
No edit summary |
No edit summary |
||
| Line 1: | Line 1: | ||
Authors: Hans-Jürgen [[Benutzer:Hschwarz|Schwarz]], Nils Mainusch | Authors: Hans-Jürgen [[Benutzer:Hschwarz|Schwarz]], Nils Mainusch | ||
<br> English version by Christa Gerdwilker | <br> English version by Christa Gerdwilker | ||
<br> | <br>back to [[Sulfate]] | ||
{{Infobox_Salt | {{Infobox_Salt | ||
| Line 30: | Line 30: | ||
|chemBehavior = | |chemBehavior = | ||
|Comments = soluble in water and glycerin,<br> insoluble in pure alcohol<br> easily loses some water, converts to thenardite at 32°C<br>abnormal blue or brown interference colors | |Comments = soluble in water and glycerin,<br> insoluble in pure alcohol<br> easily loses some water, converts to thenardite at 32°C<br>abnormal blue or brown interference colors | ||
|Literature = | |||
}} | }} | ||
<!-- | <!-- | ||
| Line 198: | Line 199: | ||
[[Category:Mirabilite]][[Category:Sulfate]][[Category:Salt]][[Category:editing]][[Category:Sulphate]] | [[Category:Mirabilite]][[Category:Sulfate]][[Category:Salt]][[Category:editing]][[Category:Sulphate]][[Category:List]] | ||
Revision as of 21:45, 15 February 2015
Authors: Hans-Jürgen Schwarz, Nils Mainusch
English version by Christa Gerdwilker
back to Sulfate
| Mirabilite[1][2] | |
| |
| Mineralogical name | Mirabilite |
| Chemical name | Sodium sulfate decahydrate |
| Trivial name | Glauber salt, Reussin, Soda Sulfate |
| Chemical formula | Na2SO4•10H2O |
| Other forms | Sodium sulfate heptahydrate Na2SO4•7H2O |
| Crystal system | monoclinic |
| Crystal structure | |
| Deliquescence humidity 20°C | 93.6% (20°C), 90% (23°C), 87% (25°C) |
| Solubility (g/l) at 20°C | 900 g/l |
| Density (g/cm³) | 1.464 g/cm³ |
| Molar volume | 219.8 cm3/mol |
| Molar weight | 322.21 g/mol |
| Transparency | transparent to opaque |
| Cleavage | perfect |
| Crystal habit | |
| Twinning | |
| Phase transition | |
| Chemical behavior | |
| Comments | soluble in water and glycerin, insoluble in pure alcohol easily loses some water, converts to thenardite at 32°C abnormal blue or brown interference colors |
| Crystal Optics | |
| Refractive Indices | nx = 1.395 ny = 1.396-1.410 nz = 1.398-1.419 |
| Birefringence | Δ = 0.04-0.023 |
| Optical Orientation | negative |
| Pleochroism | |
| Dispersion | |
| Used Literature | |
Solubility properties[edit]
Author: Stark, Jochen; Stürmer, Sylvia
].
see Sodium sulfate
Hygroscopicity[edit]
Author: Arnold, Andreas; Zehnder, Konrad
Figure 2 illustrates the influence of temperature on the deliquescence points of thenardite and mirabilite. Note the opposing curves of the graphs.
The presence of other ions, as in the case of salt mixtures, can significantly alter the equilibrium humidity parameters, i.e., the temperature and humidity conditions which initiate phase changes. Table 1 lists the experimentally determined equilibrium humidity of different salt mixtures. This shows that the equilibrium humidity of pure mirabilite is higher than that of the other salts.
| MgSO4 | Ca(NO3)2 | KNO3 | |
| Na2SO4 • 10H2O | 87(21°C) | 74 (21°C) | 81(21°C) |
Hygroscopicity
To assess the hygroscopicity of sodium sulfates, the table below compares the moisture sorption of a pure sodium sulfate and a mixture of sodium sulfate-halite at different relative humidity (RH) levels.
| storage relative RH | 87% RH. | 81% RH | 79% RH |
| Na2SO4 | 79 | 0 | 0 |
| Na2SO4+NaCl (1:1 molar mixture) |
157 | 32 | 15 |
Hydration behavior[edit]
see Sodium sulfate
Analytical evidence[edit]
Microscopy
[edit]
Laboratory analysis:
Observations of the solubility behavior through the microscope allows to verify the high water solubility of sodium sulfate and its insolubility in ethanol. Thenardite and mirabilite do not have morphological characteristics to aid their identification during simple recrystallization experiments. Instead, a broad range of different forms can be observed.
Refractive indices: nx = 1,395; ny =1.396-1.410; nz =1.398-1.419
Birefringence: Δ = 0.04-0,023
Crystal classe: monocline
Under the polarizing microscope:
The crystallization water content of the sample or its re-crystallized form depends on the ambient RH and temperature levels. In dry air (lower than 80% RH at room temperature) mirabilite loses its water of crystallization content and changes to thenardite. This process can be observed during recrystallization under the microscope. Mirabilite has characteristic abnormal interference colors which weaken during water loss and the formation of thenardite.
Differentiation from different salts:
Generally, the differentiation of certain sulfates (listed below and including thenardite) without the microchemical determination of the cations is problematic as their refractive indices are close to each other and all salts display a slight double refraction. The use of an immersion material with a nD-value of 1.48 is helpful and allows the differentiation of salts within this group. Additionally, the properties listed below can also be taken into consideration. Thenardite can be determined indirectly by the appearance of mirabilite during recrystallization to the hydrated form.
| Salt phase | Characteristics |
| Boussingaultite (NH4)2Mg(SO)4 • 6H20 | no abnormal interference colors/oblique extinction |
| Picromerite K2Mg(SO4)2 • 6H20 | no abnormal interference colors/oblique extinction |
| Bloedite Na2Mg(SO4)2 • 6H20 | all indices >1.48 / no abnormal interference colors/oblique extinction / negative optical orientation |
| Glaserite K3Na(SO4)2 | all indices >1.48 / no abnormal interference colors/oblique extinction |
| Arcanite K2SO4 | all indices >1.48 / no abnormal interference colors |
| Dashkovaite Mg(HCO2)2 • 2H2O | relatively high birefringence/ no abnormal interference colors/oblique extinction |
Mixtures:
Mixed systems Na+– Ca2+– SO4 2-: Due to its lower solubility, gypsum precipitates first during re-crystallization. The characteristic needle shaped gypsum crystals are the first to form while sodium sulfate precipitates later, the crystal growth is noticeably faster but the morphology is non-specific.
Mixed system Na+– SO4 2-– Cl-: The precipitation of both types of particles begins practically at the same time. Halite has a characteristic morphology whereas sodium sulfate occurs in extremely varying forms.
Under the polarizing microscope[edit]
- Sodium sulfate crystallization between two glass slides
Photo taken through crossed polars and red I
Photo taken through crossed polars
Weblinks
[edit]
- ↑ http://webmineral.com/data/Mirabilite.shtml accessed 29/07/2010
- ↑ http://www.mindat.org/min-2725.html accessed 29/07/2010
Literatur[edit]
| [Dana:1951] | Dana E.S. (eds.) Dana J.D. (1951): Dana's System of Mineralogy, 7, Wiley & Sons | |
| [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 () | |
| [Steiger.etal:2008] | Steiger, Michael; Asmussen, Sönke (2008): Crystallization of sodium sulfate phases in porous materials: The phase diagram Na2SO4–H2O and the generation of stress. In: Geochimica et Cosmochimica Acta, 72 (17), 4291-4306, Url | |
| [Vogt.etal:1993] | Vogt, R.; Goretzki, Lothar (1993): Der Einfluss hygroskopischer Salze auf die Gleichgewichtsfeuchte und Trocknung anorganischer Baustoffe, unveröffentlichter Bericht. | |