Carbonate

Author: Hans-Jürgen Schwarz
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Overview

The carbonate salts that are found most frequently in buildings and monuments are listed. The various salt phases are discussed in detail on separate pages, their occurrence and damage potential is explained and the deterioration patterns are illustrated and referenced.

Salt	Formula	Solubility at 20°C	Light refraction	Birefringence	Notes
Dolomite	CaMg(CO3)2	0.078 g/l (18°C)	no = 1.679-1,698 ne = 1.502-1.513	Δ = 0.177-0.185	slowly soluble in 2M HCl
Magnesite	MgCO3	0.106 g/l	no = 1.700-1.719 ne = 1.509-1.527	Δ = 0.191-0.199	very slowly soluble in 2M HCl
Nesquehonite	MgCO3•3H2O	1.79 g/l (16°C)	nx = 1.417 ny = 1.503 nz = 1.527	Δ = 0.110	hardly soluble in water pH about 10
Lansfordite	MgCO3•5H2O		nx = 1.465 ny = 1.468 nz = 1.507	Δ = 0.042	hardly soluble in water pH about 10
Hydromagnesite	Mg5(OH)2(CO3)4•4H2O		nx = 1.515-1.523 ny = 1.530-1.527 nz = 1.544-1.545	Δ = 0.029-0.022	hardly soluble in water
Natrite	Na2CO3	210 g/l	nx = 1.415 ny = 1.535 nz = 1.546	Δ = 0.131	blooms quickly in dry air and passes into the monohydrate pH about 12
Thermonatrite	Na2CO3•H2O	330 g/l	nx = 1.420 ny= 1.509 nz = 1.525	Δ = 0.105	alkaline in aqueous solution pH about 12
Trona	Na3H(CO3)2•2H2O; Na2CO3•NaHCO3•2H2O	130 g/l (0°C)	nx = 1.412 ny= 1.492 nz = 1.54	Δ = 0.128	can be produced from an aqueous solution with a high concentration of NaCl and Na2SO4 at 50-85°C pH about 10
Potash	K2CO3	1120 g/l	nx = 1.426 ny = 1.531 nz = 1.541	Δ = 0.015
Calcite	CaCO3	0.014 g/l (25°C)	no = 1.658 ne = 1.486	Δ = 0.172	well soluble in 2M HCl
Potassium carbonate dihydrate	K2CO3•2H2O	1470 g/l	nx = 1.38 ny = 1.432 nz = 1.573	Δ = 0.193
Kalicinite	KHCO3	333 g/l	nx = 1.38 ny = 1.482 nz = 1.573	Δ = 0.193	pH about 8
Potassium carbonate hexahydrate	K2CO3•6H2O
Natron	Na2CO3•10H2O	215.8 g/l	nx = 1.405 ny = 1.425 nz = 1.440	Δ = 0.035	blooms quickly in dry air and passes into the monohydrate pH about 12