Thermally driven fracture aperture variation in naturally fractured granites

Geothermal Energy

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Table 3 Granodiorite mineral composition

Phase	Mineral	Formula	\(f_{n}{^\text{a}}\)	\(\chi_{\text{Si},n}{^\text{b}}\)	\(\rho_n{^\text{b}}\) (\(\text {kg}\,\text {m}^{-3}\))
Quartz	Quartz	\(\text {SiO}_2\)	0.300	0.467	2648
Plagioclase	Albite	\(\text {NaAlSi}_3\text {O}_8\)	0.150	0.201	2620
Plagioclase	Anorthite	\(\text {CaAl}_2\text {Si}_2\text {O}_8\)	0.150	0.321	2730
K-feldspar	Microcline feldspar	\(\text {KAlSi}_3\text {O}_8\)	0.125	0.302	2620
K-feldspar	Orthoclase	\(\text {KAlSi}_3\text {O}_8\)	0.125	0.302	2560
Biotite	Annite	\(\text {KFe}_3\text {AlSi}_3\text {O}_{{10}}(\text {OH})_2\)	0.150	0.164	3260

Mineral composition considered for the calculation of fracture aperture changes, due to chemical mineral dissolution, where \({f}_n\) is the mineral volume fraction of the n-th mineral, \(\chi _{\text{Si},n}\) is the mass fraction of Si per mol of mineral n, and \(\rho _n\) is the density of mineral n
^aGrimsel granodiorite: \(\sim\) 30% quartz, \(\sim\) 30% plagioclase, \(\sim\) 25% K-feldspar, \(\sim\) 15% biotite, and minor amounts of white mica and chlorite (Stalder 1964; Schaltegger 1989)
^bSource: SciFinder: Database of chemicals (2019)