Hedenbergite

Formula : CaFe(SiO3)2

Family: 
Pyroxenes
Space group: 
Monoclinic - Prismatic H-M Symbol (2/m) Space Group: C 2/c
Dana class: 
65.1.3a.2 (65) Inosilicate Single-Width Unbranched Chains, W=1 (65.1) with chains P=2 (65.1.3a) C2/c clinopyroxenes (Ca clinopyroxenes)
High temperature: 
Based on clinopyroxene data it is possible to locate its stability around 700C and more. Stability depends also on pressure, aO2, aCO2, P.
Geological context: 
A common constituent of metamorphosed iron formations or other ferruginous siliceous sediments; common in Fe-Mn skarns. In alkalic granites, syenites, and in xenoliths in kimberlite. It is also present in smetling slags from polymetallic ores. Its an high temperature mineral.

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
248.092 68.270 (Ref.: 78hel/del,92ajoh) -2673568 (Ref.: 78hel/del,92ajoh) -2838056 (Ref.: Internal calculation) 170.289 (Ref.: 78hel/del,92ajoh) 168.87 (Ref.: 78hel/del,92ajoh)
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.
229.33 34.18 -62.80 (Ref.: 78hel/del,92ajoh)
Reaction properties

Hedenbergite + 4H+ + 2H2O ⇌ Ca+2 + Fe+2 + 2H4SiO4

298.15 K, 1 bar log10K: 19.97 ΔH°r:-141006 J·mol-1 (Ref.: Internal calculation)
T(°C) 0 25 60 100 150 200 250 300
log10K 22.15 19.97 17.32 14.86 12.41 10.42 8.72 7.13
log10K(T) = A + B·T + C·T-1 + D·log10(T) + E·T−2 (T in Kelvin)
A B C D E
-1305.918195 -0.179575 83977.294442 465.552964 -4819174.399777