I'd walk around a large 'home improvement/do it yourself' super store, like:"HomeDepot", or "Lowes"...in the title section first, then the gritt-stone/marbel cutting polsh compound section nexst, the the drill bitt, sander section nexst, last the copper tubeing section, metal HIGH TEMP cement last..place my rock specimen (sledge hammer to size of rock which fits a little loose in 4cm copper or any maleable metal tubeing(not steel!). At home place your specimen 'face oriented as you decide the plane to thin across that specimen'...place your specimen inside the tube just flush with openning...vise crimp that softmetal tube hard to hold your sample rock.
The load that tube with high temperature metal cement about that rock, let it cure.
Hacksaw off the length of tube with say 4cm tube beyond inner end of rock sample...fil in empty tube with pebbles/metalcement mattrix..something strong..let it cure.
Now you have a work piece to hold in vise (powerfully hold that specimen it the vise! Grind away under constant spray of water with ceramic diamond cmpd last.
Trick is when to stop gringing, remove specimen in its houseing mattrix...pick it free of metal cement mattrix, cement flat side down..to final diamond grinding on glass plate or whatever high temp holder you use! charlie guevara NJ,US