Editing Natron (section)

== Geological occurrence ==
Geologically, the mineral natron as well as the historical natron are formed as transpiro-[[evaporite]] minerals, i.e. crystallizing during the drying up of salt lakes rich in sodium carbonate. The sodium carbonate is usually formed by absorption of [[carbon dioxide]] from the atmosphere by a highly alkaline, sodium-rich lake [[brine]], according to the following reaction scheme:

{{block indent|NaOH<sub>(aq)</sub> + CO<sub>2</sub> → NaHCO<sub>3(aq)</sub>}}
{{block indent|NaHCO<sub>3(aq)</sub> + NaOH<sub>(aq)</sub> → Na<sub>2</sub>CO<sub>3(aq)</sub> + H<sub>2</sub>O}}

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 of [[carbon dioxide]] usually produces mixtures of [[bicarbonate]] and [[carbonate]] in solution. From such mixtures, the mineral natron (and also the historical one) will be formed only if the [[brine]] temperature during evaporation is maximally about {{convert|20|°C|°F|abbr=on}}&nbsp;– or the [[alkalinity]] of the lake is so high, that little [[bicarbonate]] is present in solution (see reaction scheme above)&nbsp;– in which case the maximum temperature is increased to about {{convert|30|°C|°F|abbr=on}}. In most cases the mineral natron will form together with some amount of [[nahcolite]] ([[sodium bicarbonate]]), resulting in salt mixtures like the historical natron.
Otherwise, the minerals [[trona]]<ref>{{cite web|url= http://webmineral.com/data/Trona.shtml|title= Trona Mineral Data}}</ref> or [[thermonatrite]] and [[nahcolite]] are 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:

* Africa
** [[Chad]]
*** shores of [[Lake Chad]]
***[[Trou au Natron]]
***Era Kohor crater on [[Emi Koussi]]
** [[Egypt]]
*** [[Wadi El Natrun]] (Natron Valley)
** [[Ethiopia]]
*** [[Shewa|Showa Province]]
** [[Niger]]
*** [[Bilma]]
** [[Tanzania]], [[Kenya]]
*** [[Lake Natron]]
* Europe
** [[Hungary]]
*** [[Bács-Kiskun|Bács-Kiskun County]], (Great Hungarian Plain)
*** [[Szabolcs-Szatmár-Bereg|Szabolcs-Szatmár-Bereg County]] (Great Hungarian Plain)
** [[Italy]]
*** [[Campania]]
*** [[Province of Naples]]
*** [[Somma-Vesuvius]] Complex
** [[Kola Peninsula]], northern [[Russia]]
*** [[Khibiny Massif]]
*** [[Lovozero Massif]]
**** [[Alluaiv]] Mountain
**** [[Kedykverpakhk]] Mountain
*** [[Umbozero]] Mine
** [[England]], UK
*** [[St Just in Penwith|St Just District]]
*** [[Botallack]]&nbsp;– [[Pendeen]] Area
* North America
** [[Canada]]
*** [[Quebec]]
**** [[Rouville Regional County Municipality|Rouville County]]
**** [[Mont-Saint-Hilaire, Quebec|Mont-Saint-Hilaire]]
*** Interior [[British Columbia]]
** [[United States]]
*** [[California]]
**** [[Inyo County, California|Inyo County]]
*** [[Nevada]]
**** [[Churchill County, Nevada|Churchill County]] ([[Soda Lakes|Soda Lake District]])
**** [[Humboldt County, Nevada|Humboldt County]]
**** [[Mineral County, Nevada|Mineral County]]
*** [[Oregon]]
**** [[Lake County, Oregon|Lake County]]
*** [[Pennsylvania]]
**** [[Karns, Pennsylvania|Karns]]
**** [[Natrona, Pennsylvania|Natrona]]
*** [[Washington (state)|Washington]]
**** [[Okanogan County, Washington|Okanogan County]]
*** [[Wyoming]]
**** [[Natrona County, Wyoming|Natrona County]]