Violet, non-pleochroic and greenish-blue, pleochroic chromium-substituted sapphirines were found in corundum-bearing spinel-websterite xenolites from the Yakutian kimberlite pipes Noyabrskaya (N) and Sludyanka (Sl), respectively. The crystallochemical formulae of sapphirine crystals from such xenolites were determined by EMP to be (Mg
3.40Fe
0.23Al
3.25Cr
0.16)
[6] Al
1.00 [6] [O
2/Al
4.53Si
1.47O
18] (N) and (Mg
2.53Fe
0.55 Mn
0.04Ti
0.03 4+ Al
3.55Cr
0.08 3+ )
[6]Al
1.00 [16] [O
2/Al
4.28Si
1.73O
18] (Sl). Single crystal spectra in the range 35000–6000 cm
1- showed a slightly polarization dependent absorption edge near 3200 cm
1- (N) or 30000 cm
1- (Sl) and unpolarized bands at 25300 and 17300 cm
1-, typical of spin-allowed transitions, derived from
4A
2g→
4T
1g and
4A
2g→
4T
2g, of Cr
3+ in octahedral sites, with point symmetry C
1, of the structure. Another weak band at 23000 cm
?1 in the sapphirine-N spectra is attributed to low symmetry splitting of the excited
4T
1 (F)-State of Cr
3+. These assignments lead to crystal field parameters Dq=1730cm
?1 and B= 685cm
?1 of Cr
3+ in sapphirine. Crystallochemical and spectroscopic arguments suggest that Cr
3+ subsitutes for Al in the M(1) or M(8) sites of the sapphirine structure. In addition to Cr
3+-transitions, spectra of Sl exhibit weak dd-bands of Fe
2+ at 10000 and 7700 cm
1-, which are unpolarized in consistency with the C
1 site symmetry of the octahedra in the structure. Spectra of Sl show also prominent, broad bands (Δv
1/2~-5000 cm
1-) at 15000 and 11000 cm
1-, which occur in E//Y(//b) and E//Z(//
c=12°) only and exhibit an intensity ratio α
Y∶α
z close to 1∶3. This result, the large half width, as well as band energy — MM distance considerations suggest that these bands originate from Fe
2+[6]-Fe
3+[6] charge-transfer transitions in wall octahedra M(1)M(2), M(6)M(7) etc., forming MM vectors of 30° with the c-axis. The lack of Fe
2+-Fe
3+ charge-transfer bands in sapphirine N might indicate a lower oxygen fugacity during the formation of the websterite from the Noyabrskaya pipe compared to that from the Sludyanka pipe.
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