  Photoluminescence spectra show that silicon impurity is present in lattice of
some nanodiamond grains (ND) of various chondrites as a silicon-vacancy (SiV)
defect. The relative intensity of the SiV band in the diamond-rich separates
depends on chemical composition of meteorites and on size of ND grains. The
strongest signal is found for the size separates enriched in small grains; thus
confirming our earlier conclusion that the SiV defects preferentially reside in
the smallest (less than 2 nm) grains. The difference in relative intensities of
the SiV luminescence in the diamond-rich separates of individual meteorites are
due to variable conditions of thermal metamorphism of their parent bodies
and/or uneven sampling of nanodiamonds populations. Annealing of separates in
air eliminates surface sp2-carbon, consequently, the SiV luminescence is
enhanced. Strong and well-defined luminescence and absorption of the SiV defect
is a promising feature to locate cold (< 250 {\deg}C) nanodiamonds in space.
