X-Ray Diffraction and Vibrational Spectroscopic Characteristics of Hydroxylclinohumite from Ruby-Bearing Marbles (Luc Yen District, Vietnam)

Table 5

Selected geometric parameters (Å) and calculated bond-valence sums (BVS) for the coordination polyhedra in (Mg_8.95Ti_0.05)(SiO₄)₄F_1.03OH_0.97 hydroxylclinohumite.

Atom1–Atom2	Bond length (Å)	BVS
Mg1C–O1,2	2.0694(10)	0.36
Mg1C–O1,2	2.0694(10)	0.36
Mg1C–O1,1	2.0908(10)	0.34
Mg1C–O1,1	2.0908(10)	0.34
Mg1C–O1,4	2.1258(10)	0.31
Mg1C–O1,4	2.1258(10)	0.31
Mean	2.095	2.02
Mg1N–O2,2	2.0700(10)	0.36
Mg1N–O1,2	2.0853(10)	0.35
Mg1N–O2,1	2.1023(11)	0.33
Mg1N–O1,1	2.1032(11)	0.33
Mg1N–O1,3	2.1165(10)	0.32
Mg1N–O2,3	2.1345(10)	0.30
Mean	2.102	1.99
Mg25−O1,3	2.0284(11)	0.40
Mg25–O2,2	2.0543(10)	0.38
Mg25–O/F*	2.0572(11)	0.35
Mg25–O2,1	2.1731(10)	0.27
Mg25–O2,3	2.1855(11)	0.26
Mg25–O2,4	2.2087(11)	0.25
Mean	2.12	1.91
Mg26−O1,2	2.0514(10)	0.38
Mg26−O1,4	2.0549(11)	0.38
Mg26−O2,3	2.0677(11)	0.36
Mg26−O1,1	2.1763(11)	0.27
Mg26−O1,3	2.1954(11)	0.26
Mg26−O1,4	2.2337(11)	0.23
Mean	2.130	1.88
Mg3/Ti3−O2,4	2.0002(11)	0.44
Mg3/Ti3−O/F*	2.0197(10)	0.38
Mg3/Ti3−O/F*	2.0393(10)	0.37
Mg3/Ti3−O2,4	2.1204(11)	0.31
Mg3/Ti3−O2,1	2.1239(11)	0.31
Mg3/Ti3−O2,2	2.1879(11)	0.26
Mean	2.082	2.07
Si1–O1,1	1.6127(10)	1.03
Si1–O1,2	1.6512(10)	0.93
Si1–O1,3	1.6347(10)	0.97
Si1–O1,4	1.6344(10)	0.97
Mean	1.633	3.90
Si2–O2,1	1.6127(10)	1.03
Si2–O2,2	1.6426(10)	0.95
Si2–O2,3	1.6380(10)	0.96
Si2–O2,4	1.6381(10)	0.96
Mean	1.633	3.90
Hydrogen bond
O–H	0.99(4)
O/F⋯O/F	2.976
O/F–H–O/F	172.49°
H⋯O/F	1.992
H⋯H	1.018
BVS (v.u.) for the oxygen atoms: O1,1 = 1.97; O1,2 = 2.02; O1,3 = 1.95, O1,4 = 1.89; O2,1 = 1.95; O2,2 = 1.95; O2,3 = 1.89; O2,4 = 1.96; O/F = 1.10

∗BVS are calculated according to the refined occupancy for oxygen [58] and fluorine atoms ([59]; updated values from http://www.ccp14.ac.uk/ccp/web-mirrors/i_d_brown/).