Halite

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Halite
Rock salt crystal.jpg
General and classification
chemical formula NaCl
Mineral class
(and possibly department) 		Halides
System no. to Strunz
and to Dana 		03.AA.20 ( 8th edition : III / A.02)
09.01.01.01
Crystallographic Data
Crystal system cubic
Crystal class ; symbol cubic hexakisoctahedral; 4 / m  3  2 / m
Space group Fm 3 m (No. 225)Template: room group / 225
Lattice parameters a  = 5.640  Å
Formula units Z  = 4
Frequent crystal faces {100}; rarely also {111}, {110}, {210}
Twinning no
Physical Properties
Mohs hardness 2 to 2.5
Density (g / cm 3 ) measured: 2.168; calculated: 2.165
Cleavage completely after {100}
Break ; Tenacity clamshell; brittle
colour colorless, white, gray, red, yellow, blue
Line color White
transparency transparent to translucent
shine Glass gloss
Crystal optics
Refractive index n  = 1.5443
Birefringence none, as it is optically isotropic
Other properties
Chemical behavior easily soluble in water
Special features salty taste, fluorescence

Halite (from ancient Greek ἅλς hals , Gen. ἁλός halos , "salt") is a common mineral from the mineral class of simple halides . It crystallizes in the cubic crystal system with the chemical composition NaCl and is therefore chemically sodium chloride .

Halite usually develops cube-shaped crystals and large, granular to massive, rarely also fibrous mineral aggregates . In its pure form, halite is colorless and transparent. However, due to multiple refraction due to its polycrystalline design , it can also appear white and, due to foreign admixtures or lattice construction defects, it can take on a gray, brownish, yellow to red or bluish color, with the transparency decreasing accordingly.

Halite is a rock forming minerals and instrumental in building the rock salt - deposits involved. Rock salt is a monomineral rock, which, apart from small admixtures of other salt minerals such as anhydrite , gypsum , sylvine and others, is composed almost exclusively of the mineral halite. That is why “rock salt” and “halite” are often used synonymously in German colloquial language despite inaccuracy.

Etymology and history

The name Halit is derived from the ancient Greek word hals ἅλς (plural hales ἅλες , neuter halas ἅλας ) for salt and the ending -itos -ιτος and therefore means “salty” or “concerning salt” (see also halogens ).

The table salt obtained from salt domes or salt pans has been a sought-after commodity since ancient times, which was exported from the places of manufacture to regions with little salt on so-called salt roads. Sometimes it was so valuable that it was also known as white gold .

classification

Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the halite belonged to the mineral class of "halides" and there to the department of "simple halides" (with metal: halogen = 1: 1), where it was named after the "Halit series" with the system no. III / A.02 and the other members bromargyrite , carobbiite , chlorargyrite , sylvin and villiaumite .

In the Lapis mineral directory according to Stefan Weiß, which, out of consideration for private collectors and institutional collections, is still based on this classic system of Karl Hugo Strunz , the mineral was given the system and mineral number. III / A.02-30 . In the “Lapis system”, this also corresponds to the “Simple halides” section, where halite, together with bromogyrite, carobbiite, chlorargyrite, griceit , sylvin and villiaumite, forms an independent but unnamed group.

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and was updated by the International Mineralogical Association (IMA) until 2009, classifies halite in the somewhat more refined section of "simple halides without H 2 O". This is further subdivided according to the molar ratio of metal (M) to halogen (X), so that the mineral can be found in the sub-section “M: X = 1: 1 and 2: 3”, where it also gives it its name the "Halitgruppe" with the system no. 3.AA.20 and the other members Carobbiit, Griceit, Sylvin and Villiaumit.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns halite to the class and division of the same name of "halides". Here he is also in the "Halite group" named after him with the system no. 01/09/01 to be found in the subsection " Anhydrous and hydrous halides with the formula AX ".

Chemism

Theoretically, halite consists of 39.4% sodium and 60.6% chlorine and the compound is usually very pure if it forms sediment , which means that there is no diagonal incorporation of other elements. For example, the incorporation of bromine as a replacement for chlorine is less than 0.05%. However, the sedimentary formation promotes mechanical inclusions ( inclusions ) and impurities.

At over 500 ° C, as is the case with high-temperature fumaroles , however, there is the possibility of gapless solid solution formation between halite and the potassium chloride mineral sylvin .

Crystal structure

Crystal structure of halite
gray = Na + ; Green = Cl -

Halite crystallizes cubically in the space group Fm 3 m (space group no. 225) with the average lattice parameter a  = 5.640  Å determined in several measurements from 2004 and four formula units per unit cell . Template: room group / 225

The NaCl structure consists of an ion lattice with two face-centered cubic crystal lattices , one inside the other and offset by half an edge length . Each sodium cation is octahedral surrounded by 6 chloride anions and each chloride anion is also octahedral surrounded by 6 sodium cations. This type of crystal structure through ionic bonding also explains the low hardness combined with complete cleavage and brittleness, as on the one hand the binding forces of the relatively large ions are only weak and on the other hand, even with low shear stress, ions with the same, repelling electrical charge collide with each other and the crystal drive the place apart. Its crystal structure is isotypic with galena .

properties

colour

When hematite is deposited , the halite crystals take on a reddish color; when limonite is embedded, they take on a more yellowish color . Additions of clay minerals or bitumen make halite appear gray to brownish-black.

In the case of blue-violet halites, the color of which usually has a cloudy appearance, the color is caused by colloidally distributed sodium ions in the crystal. The reason for this is the radiation of radioactive substances that can displace sodium ions onto interstitial spaces and thereby create color centers in the crystal. Similar discolorations can also be created artificially by exposing halite crystals to ionizing radiation or by heating them and passing electrical direct current through them.

fluorescence

Halite with red-violet fluorescence from the Wieliczka Mine, Małopolskie, Poland (size: 11.0 × 6.8 × 4.0 cm)

Under UV light , some halites show fluorescence of different colors , which, however, depends on the wavelength of the UV radiation and the type of embedded elements and thus on the location.

In general, a reddish fluorescence is indicated under short-wave UV light, but it can also be greenish if organic substances are stored. Reddish or greenish-orange fluorescence can also occur under long-wave UV light.

Other properties

Halite is easily soluble in water and has the typical salty taste. It is also an excellent conductor of heat and, when heated, also a good electrical conductor .

The melting point of halite is 801 ° C.

Chemically pure halite is not hygroscopic , but it does acquire this property of absorbing moisture from the environment by adding the extremely hygroscopic mineral bischofite (MgCl 2 · 6H 2 O).

Modifications and varieties

As Huantajayit a Halit- variety of about 3 to 11% Chlorargyrit designated (AgCl).

Education and Locations

Fibrous halite crystals from Fayum , Egypt
Halite stained pink by bacteria on a crust of Nahcolith from Searles Lake, San Bernardino County , California, USA

Halite occurs in massive, granular or crystalline form in sedimentary rocks . It is formed by the crystallization of sea water and is associated with other less water-soluble minerals calcite and anhydrite in the resulting layers of deposits ( evaporite ) . Anhydrite Ca [SO 4 ] emerged from the originally crystallized gypsum Ca [SO 4 ] • 2 H 2 O through dehydration. Rock salt deposits that have been sunk deeply behave plastically under pressure and often deform into huge structures, salt walls or salt domes. Rock salt is also rarely found as a sublimate in volcanic vents or fumaroles on Etna and Vesuvius in Italy, among others .

So far (as of 2015) almost 1000 sites for halite are known worldwide. Important sites in Central Europe are the huge salt deposits from the Upper Permian ( Zechstein ) in the subsurface of Northern Germany (" Zechstein Sea "), some with potash salts. Extraction of rock salt still takes place near Bernburg . B. in Stassfurt . In addition, the middle Muschelkalk in Baden-Württemberg leads to rock salt layers (Heilbronn, Stetten on the Swabian Alb), which continue into Switzerland (Rheinfelden, Schweizerhalle, particularly powerfully drilled near Porrentruy). In Austria , Bad Aussee ( Styria ) and earlier Hall ( Tyrol ), Hallein ( Salzburg ) and Hallstatt ( Salzkammergut ) should be mentioned. The salt dome in Wieliczka, Poland, has also become famous .

The largest salt crystals in the world with edge lengths of over 1.10 m can be found in the crystal grotto in the Merkers adventure mine in Thuringia . The halite cubes from the Wieliczka and Bochnia sites in Poland reach an edge length of at least 10 cm .

Other locations include Afghanistan , Egypt , Algeria , Antarctica , Argentina , Ethiopia , Australia , Azerbaijan , Belgium , Bolivia , Bosnia and Herzegovina , Brazil , Chile , China , Denmark , Germany , Dominican Republic , Djibouti , Finland , France , Greece , India , Iran , Iceland , Italy , Japan , Canada , Kazakhstan , Kenya , Colombia , Democratic Republic of the Congo , Morocco , Mexico , Namibia , Netherlands , New Zealand , Norway , Austria , Pakistan , the entire Palestine region (Israel, Golan Heights, Gaza Strip , West Bank and Jordan), Panama , Peru , Poland , Portugal , Romania , Russia , Saudi Arabia , Sweden , Switzerland , Serbia , Slovakia , Spain , South Africa , Syria , Tanzania , Czech Republic , Tunisia , Turkey , Turkmenistan , Ukraine , Hungary , Venezuela , the United Kingdom (Great Britain), the United States (USA) and Belarus ( Belarus ). Outside the earth , the mineral could still be detected on the moon in the rock samples of the Mare Crisium .

use

Heart-shaped tealight candle holder made from a lump of halite

The halite obtained from rock salt, like sodium chloride obtained in other ways, is used as table salt , road salt , in the food industry and also in medicine . It is therefore of great economic importance.

In Germany, Austria, the USA and Canada in particular , rock salt is still extracted in salt mines by mining or leaching (caverns). Its mining in the Salzkammergut is already documented for the time of the Celts . The largest rock salt mine in Germany is located under the city of Heilbronn . Together, the dismantled chambers are over 400 km long.

Furthermore, halite or rock salt is the most important raw material for the extraction of elemental sodium and chlorine , which are produced by means of fused- salt electrolysis .

See also

literature

Web links

Commons : Halite  - collection of images, videos and audio files

Individual evidence

  1. ^ A b c David Barthelmy: Halite Mineral Data. In: webmineral.com. Retrieved October 14, 2019 .
  2. ^ A b c Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  150 (English).
  3. ^ Helmut Schrätze , Karl-Ludwig Weiner : Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp.  311 .
  4. ↑ a b c d e Halite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 63  kB ; accessed on October 14, 2019]).
  5. ↑ Halite. In: mindat.org. Hudson Institute of Mineralogy, accessed October 14, 2019 .
  6. ↑ August Friedrich Pauly : Salt . In: Paulys Realencyclopadie der classischen Antiquity Science (RE). Volume IA, 2, Stuttgart 1920, Sp. 2075-2099.
  7. ↑ Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties. Status 03/2018 . 7th, completely revised and supplemented edition. Weise, Munich 2018, ISBN 978-3-921656-83-9 .
  8. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed October 14, 2019 .
  9. ↑ a b Hans Jürgen Rösler : Textbook of Mineralogy . 4th revised and expanded edition. German publishing house for basic industry (VEB), Leipzig 1987, ISBN 3-342-00288-3 , p.  359 .
  10. ^ A b c d Helmut Schrätze , Karl-Ludwig Weiner : Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp.  313 .
  11. ↑ Martin Okrusch, Siegfried Matthes: Mineralogie. An introduction to special mineralogy, petrology and geology . 7th, completely revised and updated edition. Springer, Berlin [a. a.] 2005, ISBN 3-540-23812-3 , pp. 46 .
  12. ^ Helmut Schrätze , Karl-Ludwig Weiner : Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp.  314 .
  13. ^ Helmut Schrätze , Karl-Ludwig Weiner : Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp.  317 .
  14. ↑ Localities for Halite. In: mindat.org. Hudson Institute of Mineralogy, accessed October 14, 2019 .
  15. ↑ Mineral Atlas: Mineral Records
  16. ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Dörfler Natur ). Edition Dörfler im Nebel-Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 71 .
  17. ↑ List of locations for halite from the Mineralienatlas and Mindat , accessed on October 14, 2019
  18. ^ Helmut Schrätze , Karl-Ludwig Weiner : Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp.  316 .