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Author: Kirsten Linnow

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Thecotrichite 19082010-9.jpg
Mineralogical name Thecotrichite
Chemical name Tricalcium triacetate chloride dinitrate heptahydrate
Trivial name
Chemical formula Ca3(CH3COO)3Cl(NO3)2•7H2O
Other forms
Crystal system
Crystal structure
Deliquescence humidity 20°C 85% (20°C)
Solubility (g/l) at 20°C
Density (g/cm³)
Molar volume
Molar weight 582.936 g/mol
Crystal habit
Phase transition
Chemical behavior
Comments found on calcareous museum objects and archaeological ceramic objects]]
Crystal Optics
Refractive Indices nx = 1.491 ± 0.001
nz = 1.494 ± 0.003
Optical Orientation
Used Literature

Phase diagram of the quaternary system Ca(CH3COO)2–CaCl2–Ca(NO3)2–H2O

The number of the stability fields refer to a salt phase, which is in equilibrium with the saturated solutions of a stability field, as follows:
(1) CaCl2 • 6H2O, (2) CaCl2 • 4H2O, (3) CaCl(NO3) • 2H2O, (4) Ca(NO3)2 • 3H2O, (5) Ca(NO3)2 • 4H2O, (6) Ca2(CH3COO)3(NO3) • 2H2O, (7) Ca(CH3COO)2 • H2O, (8) Ca(CH3COO)Cl • 5H2O, (9) Ca3(CH3COO)3Cl(NO3)2 • 7H2O.
Point T in the phase diagram represents the composition of the triple salt thecotrichite (Ca3(CH3COO)3Cl(NO3)2 • 7H2O).

The isothermal phase diagram of the quaternary system Ca(CH3COO)2–CaCl2–Ca(NO3)2–H2O (25°C) [Linnow:2007]Title: Salt damage in porous materials: An RH XRD investigation
Author: Linnow, Kirsten
Link to Google Scholar
is shown as Jännecke projection for the anhydrous level. All solution compositions are given as molar ratios of Ca(CH3COO)2, CaCl2 and Ca(NO3)2. The corners of the triangle represent the three pure salts, the sides represent the three ternary systems Ca(CH3COO)2–CaCl2–H2O, Ca(CH3COO)2–Ca(NO3)2–H2O and CaCl2–Ca(NO3)2–H2 while the inner surface represents all solution compositions where the three salts are involved.

The inner lines delimit the stability fields of a given salt phase. The stability fields represent all solution compositions, which are saturated with respect to only a single salt phase. The univariant lines represent the solution compositions where two salt phases are in equilibrium with the solution.

According to Gibbs’ phase rule in the quaternary system a maximum of three different salt phases can coexist in solution equilibrium. It follows that for each possible combination of three salt phases in the solid phase, only one saturated solution composition is possible. These solution combinations are represented by intersections of the univariant lines.



[Linnow:2007]Linnow, Kirsten (2007): Salt damage in porous materials: An RH XRD investigation. Dissertation, Institut für Anorganische und Angewandte Chemie, Universität Hamburg, UrlLink to Google Scholar