I rather think that we are looking at the material used in grafting an implant. I assume the PCintern, or whoever it was, could fill in the details, but in brief, sometimes it is necessary to fill the socket void with a 'powdered bone' to bond the implant. This material is put into the void, stitched over and allowed to fuse with the base of the implant (which can be titanium or ceramic) before placing the actual stud upon which the final appliance (tooth) is cemented (bonded). It can take several office visits to do this correctly hence the cost. You really don't just drill and tap the empty socket.
Implant technology has come a long way and there are lots of skilled folk out there. There are also a lot of not so skilled folk who can do some real long term nerve damage if they don't know what they are doing. If you think having a tooth pulled is painful, having a bad implant removed is orders of magnitude worse.
Disclaimer:
I am not a dentist, dental hygienist, dental receptionist, nor in any other way skilled in this procedure, or I play one on TV.