Dawsonite

Dawsonite is a mineral composed of sodium aluminium carbonate hydroxide, chemical formula NaAlCO₃(OH)₂. It crystallizes in the orthorhombic crystal system. It is not mined for ore. It was discovered in 1874 during the construction of the Redpath Museum in a feldspathic dike on the campus of McGill University on the Island of Montreal, Canada.^[2] It is named after geologist Sir John William Dawson (1820–1899).^[3]

Dawsonite
Dawsonite from Mont Saint-Hilaire, Rouville RCM, Montérégie, Québec, Canada
General
Category	Carbonate minerals
Formula	NaAlCO3(OH)2
IMA symbol	Dws[1]
Strunz classification	5.BB.10
Dana classification	16a.03.08.01
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Imam
Identification
Formula mass	144.00 g/mol
Color	white
Crystal habit	encrustations or radial
Cleavage	perfect on {110}
Fracture	uneven
Mohs scale hardness	3
Luster	vitreous
Streak	white
Diaphaneity	transparent
Specific gravity	2.436
Refractive index	nα = 1.466 nβ = 1.542 nγ = 1.596
Birefringence	δ = 0.130
2V angle	77°
References	[2][3]

The type material is preserved in the collection of the Redpath Museum.^[2]

See also

• Dihydroxialumini sodium carbonate, the commercial (artificial) form, used as an antacid
• List of minerals
• List of minerals named after people