consists of a pedestal 4 on which is mounted a furnace chamber 3 connected to heating means which enable heating to be effected within the furnace 3 within the furnace chamber 3 is a seed holder arm 6 arranged to be located such that its distal end can be positioned within a melt receptacle 10 located on the pedestal 4 at the distal free end of the free arm is a seed crystal 12 that is arranged to be lowered into the melt receptacle 10 in use the apparatus in fig1 shows a growing crystal 14 connected to the seed crystal 12 growing in a melt solution present within the melt receptacle 10 the seed holder arm 6 is rotatable and is such that rotation may be effected during growth of the crystal 14 in use the airspace within the furnace 3 is a controlled atmosphere in which the heat within the furnace may be adjusted as desired the seed arm 6 is also movable upwardly and downwardly with respect of the pedestal 4 such that during growth of the crystal 14 the seed arm may be retracted slowly from the melt receptacle 10 in order that further growth of the crystal 14 may be effected and a continual temperature gradient of the seed 12 and crystal 14 effected in order to enable continued growth of the crystal 14 in alternative embodiments of the apparatus 2 a cold finger may or may not be used to control grain nucleation and growth in the apparatus 2 additionally the seed crystal may be placed on an exposed surface of the precursor pellet compact at room temperature rather.