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Natron

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For the compositing software, seeNatron (software).For the lake in Africa, seeLake Natron.For other, seeNatron (disambiguation).
Natron
Natron deposits in the Era Kohor crater in theTibesti Mountains,Chad
General
CategoryCarbonate mineral
Formula
(repeating unit)		Na2CO3·10H2O
IMA symbolNt[1]
Strunz classification5.CB.10
Dana classification15.01.02.01
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(sameH-M symbol)
Space groupP2/m
Unit cella = 12.75 Å, b = 9 Å, c = 12.6 Å
β = 115.85°
Identification
ColourColourless to white, greyish, yellowish; colourless in transmitted light.
Crystal habitcrystalline, granular, and columnar crusts
Twinningon {001}
CleavageOn {001} distinct; on {010} imperfect; on {110} in traces.
FractureConchoidal
TenacityBrittle
Mohs scalehardness1 – 1.5
LustreVitreous
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity1.478
Optical propertiesBiaxial (−)
Refractive indexnα= 1.405 nβ= 1.425 nγ= 1.440
Birefringenceδ = 0.035
2V angleMeasured: 71°, Calculated: 80°
SolubilitySoluble in water
References[2][3][4]

Natronis a naturally occurring mixture ofsodium carbonatedecahydrate (Na2CO3·10H2O, a kind ofsoda ash) and around 17%sodium bicarbonate(also called baking soda, NaHCO3) along with small quantities ofsodium chlorideandsodium sulfate.Natron is white to colourless when pure, varying to gray or yellow with impurities. Natron deposits are sometimes found in saline lake beds which arose in arid environments. Throughout history natron has had many practical applications that continue today in the wide range of modern uses of its constituent mineral components.

In modernmineralogythe termnatronhas come to mean only the sodium carbonate decahydrate (hydrated soda ash) that makes up most of the historical salt.

Natron deposits, Trou au Natron, Tibesti, Chad

Etymology

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TheEnglishandGermanwordnatronis aFrenchcognatederived from theSpanishnatrónthroughLatinnatriumandGreeknitron(νίτρον). This derives from theAncient Egyptianwordnṯrj.Natronrefers toWadi El Natrunor Natron Valley in Egypt, from which natron was mined by the ancient Egyptians for use in burial rites. The modern chemical symbol forsodium,Na,is an abbreviation of that element'sNeo-Latinnamenatrium,which was derived fromnatron.The name of the chemical elementNitrogenis also a cognate to natron, it derives from Greeknitronand-gen (a producer of something, in this caseNitric acid,which was produced fromniter). Niter was also an obsolete name for natron because in earlier times, both minerals used to be confused with each other.

Importance in antiquity

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Afaiencevase fabricated in part from natron, dating to theNew Kingdom of Egypt(c. 1450–1350 BC)

Historical natron was harvested directly as a salt mixture from dry lake beds inancient Egypt,and has been used for thousands of years as a cleaning product for both the home and body. Blended with oil, it was an early form ofsoap.Itsoftens waterwhile removing oil and grease. Undiluted, natron was a cleanser for the teeth and an earlymouthwash.The mineral was mixed into earlyantisepticsfor wounds and minor cuts. Natron can be used to dry and preserve fish and meat. It was also an ancient household insecticide, and was used for making leather as well as a bleach for clothing.

The mineral was used duringmummificationceremonies in ancient Egypt because it absorbs water and behaves as a drying agent. Moreover, when exposed to moisture, thecarbonatein natron increasespH(raisesalkalinity), which creates a hostile environment for bacteria. In some cultures, natron was thought to enhance spiritual safety for both the living and the dead. Natron was added tocastor oilto make asmokeless fuel,which allowed Egyptian artisans to paint elaborate artworks inside ancient tombs without staining them with soot.

The Pyramid Texts describe how natron pellets were used as funerary offerings in the rites for the deceased pharaoh, "N". The ceremony required two kinds of natron, one sourced from northern (Lower) and one from southern (Upper) Egypt.

Smin,sminopens thy mouth. One pellet of natron.
O N., thou shalt taste its taste in front of thesḥ-ntr-chapels. One pellet of natron.
That which Horus spits out issmin.One pellet of natron.
That which Set spits out issmin.One pellet of natron.
That which the two harmonious gods (spit out) issmin.One pellet of natron.
To say four times: Thou hast purified thyself with natron, together with Horus (and) the Followers of Horus. Five pellets of natron from Nekheb, Upper Egypt.
Thou purifiest (thyself); Horus purifies (himself). One pellet of natron. Thou purifiest (thyself); Set purifies (himself). One pellet of natron.
Thou purifiest (thyself); Thot purifies (himself). One pellet of natron. Thou purifiest (thyself); the god purifies (himself). One pellet of natron.
Thou also purifiest (thyself)—thou who art among them. One pellet of natron.
Thy mouth is the mouth of a sucking calf on the day of his birth.
Five pellets of natron of the North, Wadi Natrûn (št-p.t)[5]

Natron is an ingredient for making a distinct color calledEgyptian blue,and also as thefluxinEgyptian faience.It was used along withsandandlimein ceramic and glass-making by the Romans and others at least until AD 640. The mineral was also employed as a flux to solder precious metals together.

Decline in use

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Most of natron's uses both in the home and by industry were gradually replaced with closely related sodium compounds and minerals. Natron'sdetergentproperties are now commercially supplied bysoda ash(pure sodium carbonate), the mixture's chief compound ingredient, along with other chemicals. Soda ash also replaced natron inglass-making.Some of its ancient household roles are also now filled by ordinarybaking soda,which issodium bicarbonate,natron's other key ingredient.

Chemistry of hydrated sodium carbonate

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Natron is also the mineralogical name for the compound sodium carbonate decahydrate (Na2CO3·10H2O), which is the main component in historical natron.[4]Sodium carbonate decahydrate has aspecific gravityof 1.42 to 1.47 and aMohs hardnessof 1. It crystallizes in themonoclinic-domaticcrystal system,typically forming efflorescences and encrustations.

The termhydrated sodium carbonateis commonly used to encompass the monohydrate (Na2CO3·H2O), the decahydrate and the heptahydrate (Na2CO3·7H2O), but is often used in industry to refer to the decahydrate only. Both the hepta- and the decahydrate effloresce (lose water) in dry air and are partially transformed into the monohydratethermonatriteNa2CO3·H2O.

As a source of soda ash

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Sodium carbonate decahydrate is stable at room temperature but recrystallizes at only 32 °C (90 °F) to sodium carbonate heptahydrate, Na2CO3·7H2O, then above 37–38 °C (99–100 °F) to sodium carbonate monohydrate, Na2CO3·H2O. This recrystallization from decahydrate to monohydrate releases much crystal water in a mostly clear, colorless salt solution with little solidthermonatrite.The mineral natron is often found in association withthermonatrite,nahcolite,trona,halite,mirabilite,gaylussite,gypsum,andcalcite. Most industrially produced sodium carbonate is soda ash (sodium carbonate anhydrate Na2CO3) which is obtained by calcination (dry heating at temperatures of 150 to 200 °C) of sodium bicarbonate, sodium carbonate monohydrate, ortrona.

Geological occurrence

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Geologically, the mineral natron as well as the historical natron are formed as transpiro-evaporiteminerals, i.e. crystallizing during the drying up of salt lakes rich in sodium carbonate. The sodium carbonate is usually formed by absorption ofcarbon dioxidefrom the atmosphere by a highly alkaline, sodium-rich lakebrine,according to the following reaction scheme:

NaOH(aq)+ CO2→ NaHCO3(aq)
NaHCO3(aq)+ NaOH(aq)→ Na2CO3(aq)+ H2O

Pure deposits of sodium carbonate decahydrate are rare, due to the limited temperature stability of this compound and due to the fact that the absorption ofcarbon dioxideusually produces mixtures ofbicarbonateandcarbonatein solution. From such mixtures, the mineral natron (and also the historical one) will be formed only if thebrinetemperature during evaporation is maximally about 20 °C (68 °F) – or thealkalinityof the lake is so high, that littlebicarbonateis present in solution (see reaction scheme above) – in which case the maximum temperature is increased to about 30 °C (86 °F). In most cases the mineral natron will form together with some amount ofnahcolite(sodium bicarbonate), resulting in salt mixtures like the historical natron. Otherwise, the mineralstrona[6]orthermonatriteandnahcoliteare commonly formed. As the evaporation of a salt lake will occur over geological time spans, during which also part or all of the salt beds might redissolve and recrystallize, deposits of sodium carbonate can be composed of layers of all these minerals.

The following list may include geographical sources of either natron or other hydrated sodium carbonate minerals:

See also

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References

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  1. ^Warr, L.N. (2021)."IMA–CNMNC approved mineral symbols".Mineralogical Magazine.85(3): 291–320.Bibcode:2021MinM...85..291W.doi:10.1180/mgm.2021.43.S2CID235729616.
  2. ^"Natron Mindat".mindat.org.Retrieved2022-11-28.
  3. ^"Natron Handbook"(PDF).Retrieved2022-11-28.
  4. ^ab"Natron Mineral Data".webmineral.com.Retrieved2022-11-26.
  5. ^www.sacred-texts.com/egy/pyt/pyt05.htmThe Pyramid Texts,Utterance 35. Translated by Samuel A. B. Mercer, 1952. Accessed 9 April 2020.
  6. ^"Trona Mineral Data".
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