Trona
General
Category	Carbonate mineral
Formula (repeating unit)	Na2CO3·NaHCO3·2H2O
IMA symbol	Tn[1]
Strunz classification	5.CB.15
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	C2/c (no. 15)
Identification
Color	Colorless (in transmitted light) or white, grey-white, also grey to yellowish grey, light yellow
Crystal habit	Columnar, fibrous and massive.
Cleavage	[100] perfect, [111] and [001] indistinct
Fracture	Brittle – subconchoidal
Mohs scale hardness	2.5
Luster	Vitreous
Streak	White
Diaphaneity	Translucent
Specific gravity	2.11–2.17
Optical properties	Biaxial (−)
Refractive index	nα = 1.412 nβ = 1.492 nγ = 1.540
Birefringence	δ = 0.128
Solubility	Soluble in water
Other characteristics	May fluoresce under short wavelength ultraviolet
References	[2][3][4][5]

Trona (trisodium hydrogendicarbonate dihydrate, also sodium sesquicarbonate dihydrate, Na₂CO₃·NaHCO₃·2H₂O) is a non-marine evaporite mineral.^[4][6] It is mined as the primary source of sodium carbonate in the United States, where it has replaced the Solvay process used in most of the rest of the world for sodium carbonate production. Turkey is also a major producer.

Etymology

The word entered English by way of either Swedish (trona) or Spanish (trona), with both possible sources having the same meaning as in English: the mineral natron from North Africa. Both the Spanish and Swedish^[7] terms derive from the Arabic trōn, which in turn derives from Arabic natron and Hebrew נתרן (natruna), which comes from ancient Greek νιτρον (nitron), derived ultimately from ancient Egyptian ntry (or nitry'’).^{[citation needed]}

Natural deposits

Trona is found at Owens Lake and Searles Lake, California; the Green River Formation of Wyoming and Utah; the Makgadikgadi Pans in Botswana and in the Nile Valley in Egypt.^[8] The trona near Green River, Wyoming, is the largest known deposit in the world and lies in layered evaporite deposits below ground, where the trona was deposited in a lake during the Paleogene Period.^[9] Trona has also been mined at Lake Magadi in the Kenyan Rift Valley for nearly 100 years. The northern part of Lake Natron is covered by a 1.5 m thick trona bed,^[10] and occurs in 'salt' pans in the Etosha National Park in Namibia.^[11] The Beypazari region in the Ankara Province of Turkey has some 33 trona beds in two fault-bound lensoid bodies in and above oil shales of the Lower Hirka Formation (16 in the lower and 17 in the upper body).^[12] The Wucheng basin trona mine, Henan Province China has some 36 trona beds (693–974 m deep), the lower 15 beds are 0.5–1.5 m thick, thickest 2.38 m; the upper 21 beds are 1–3 m thick, with a maximum of 4.56 m hosted and underlain by dolomitic oil shales of the Wulidui Formation.^[13]

Trona has also been found in magmatic environments.^[14] Research has shown that trona can be formed by autometasomatic reactions of late-magmatic fluids or melts (or supercritical fluid-melt mixtures), with earlier crystallized rocks within the same plutonic complex, or by large-scale vapor unmixing in the very final stages of magmatism.^[14]

Crystal structure

The crystal structure of trona was first determined by Brown et al. (1949).^[15] The structure consists of units of 3 edge-sharing sodium polyhedra (a central octahedron flanked by septahedra), cross-linked by carbonate groups and hydrogen bonds. Bacon and Curry (1956)^[16] refined the structure determination using two-dimensional single-crystal neutron diffraction, and suggested that the hydrogen atom in the symmetric (HC₂O₆)³⁻ anion is disordered. The environment of the disordered H atom was later investigated by Choi and Mighell (1982)^[17] at 300 K with three-dimensional single-crystal neutron diffraction: they concluded that the H atom is dynamically disordered between two equivalent sites, separated from one another by 0.211(9) Å. The dynamically disordered H atom was reinvestigated at low temperature by O'Bannon et al. 2014 and they concluded that it does not order at temperatures as low as 100K.^[18]

Uses

• Trona is a common source of soda ash, which is a significant economic commodity because of its applications in manufacturing glass, chemicals, paper, detergents, and textiles.
• It is used to condition water.
• It is used to remove sulfur from both flue gases and lignite coals.^[19][20]
• It is a product of carbon sequestration of flue gases.^[21]
• It is also used as a food additive.^[22]

Mining operations

• Rio Tinto – Owens Lake
• Magadi Soda Company
• Searles Valley Minerals Inc.
• Solvay^[23]
• Tata Chemicals^[23]
• Genesis Alkali formerly Tronox Alkali^[23] formerly FMC Corporation
• General Chemical
• Ciner Wyoming^[23] formerly OCI Chemical Corp.
• ANSAC
• Eti Soda, Turkey
• Kazan Soda Elektrik, Turkey
• Church & Dwight – Green River Mine^[24][25]
• Intrepid Potash^[26]
• Simplot^[27]