Larnite(alpha)

Formula : Ca2SiO4

Space group: 
Monoclinic - Prismatic H-M Symbol (2/m) Space Group: P 21/n
Dana class: 
51.5.1.1 (51) Nesosilicate Insular SiO4 Groups Only (51.5) with cations in >[6] coordination (51.5.1) Dana Group
High temperature: 
5 polymorphs of Ca2SiO4 exist at ordinary pressures, with decreasing T: a, a'H, a'L, b, g. During the heating of clinker, larnite (or belite) appears at around 900C. Only beta larnite is found in nature. Alpha larnite is stable just below the melting point, 2130C, and above 1420C. Gamma phase is stable below 675C, with a crystal structure similar to that of olivine.
Geological context: 
In contact with metamorphic terranes involving sedimentary carbonate rocks.

Dernière mise à jour le 25.01.2021

THERMODYNAMICS

Individual properties (298.15 K)
M
g·mol-1
 V°
cm3·mol-1
 ΔGºf
J·mol-1
 ΔHºf
J·mol-1
 Sº
J·mol-1·k-1
 CP
J·mol-1·K-1
172.239 51.600 (Ref.: 78hel/del,60kel) -2192007 (Ref.: Internal calculation) -2306700 (Ref.: 95rob/hem) Robie R.A., and Hemingway B.S., 1995. Thermodynamic properties of minerals and related substances at 298.15 K and 1 Bar (105 Pascals) pressure and at higher temperatures. U.S. Geol. Survey Bull., 2131, 461 pp. 127.612 (Ref.: 78hel/del,60kel) 128.58 (Ref.: 78hel/del,60kel)
CP(T) = a + b·T + ·c·T-2 (T in Kelvin)
a
J·mol-1·K-1
 b * 103
J·mol-1·K-2
 c * 10-5
J·K·mol-1
 Maier Kelley Ref.
145.90 40.75 -26.19 (Ref.: 78hel/del,60kel)
Reaction properties

Larnite(alpha) + 4H+ ⇌ 2Ca+2 + H4SiO4

298.15 K, 1 bar log10K: 39.04 ΔH°r:-238161 J·mol-1 (Ref.: 95rob/hem) Robie R.A., and Hemingway B.S., 1995. Thermodynamic properties of minerals and related substances at 298.15 K and 1 Bar (105 Pascals) pressure and at higher temperatures. U.S. Geol. Survey Bull., 2131, 461 pp.
T(°C) 0 25 60 100 150 200 250 300
log10K 42.82 39.04 34.64 30.59 26.58 23.36 20.66 18.27
log10K(T) = A + B·T + C·T-1 + D·log10(T) + E·T−2 (T in Kelvin)
A B C D E
-899.089415 -0.130138 63335.054606 322.961682 -3079344.605019