  Single crystals of MgB2 and Mg(B1-xCx)2 have been grown using cubic anvil
technique. Tc values vary in a wide range (39-9 K) with carbon content varying
from 0 up to 16%. Using SiC as the precursor leads to C and not to Si
substituted crystals. Micro-hardness measurements performed on MgB2 single
crystals give average value of 1100 kg/mm2.
