You can't "slice" crystalline calcium carbonate, but you can easily abrade
it, as illustrated by those "shell doctors" who reshape and smooth the
chipped lips of expensive cone shells using sandpaper or a small grinding
wheel.  In my admittedly sparse experience in "drilling" shells, I have
found it necessary to keep this principle in mind.  An ordinary drill
doesn't work on shells because the tip of such a drill actually consists of
two tiny, sharp blades designed to slice through wood or metal - but not
shell.  I have had success with a tiny bit made of carborundum or some
similar material (the same stuff grindstones or whetstones are made of), in
a small, hand-held high speed rotary tool such as those made by Dremel.
Dremel also makes a wide range of tiny bits and accessories for such
purposes.  There are other brands too.  I'm just most familiar with the
Dremel line.  With such a tool you can easily bore (not actually "drill") a
tiny, smooth hole through just about anything - even glass.

Paul M.