Although rocks from the outside can give clues about their internal anatomy, the only real way to know is to whack it open with a rock hammer or saw  it with diamond blade.  Using a chisel or rock hammer to split a stone can be helpful in the field as a way of checking what you have, but once you crack it, you may ruin it!

Compared to saws that cut wood or metal, rock saws can be expensive. Anything that is tied to "lapidary" tends to be that way. I suppose two things are at work here, 1) The number of manufacturers and number of consumers of rock saws are an order of magnitude smaller that wood or metal buyers.  As a specialty item, the costs are higher as these boutique  manufacturers have lower volume and higher overhead costs per machine. 2) Anyone selling rock tools to the hobbyist knows that there is a special drive/desire on the part of the consumer who may be willing to pay more to get the tool they want!  If you take a tile saw, for example, that works just as well on rocks as it does tile and sell it as a lapidary device you will see the price go from $100 to $300 with little change in the function or utility of the tool!

Tile saws pull water from a tray under the blade and spew a spray onto the blade and rock and you!  I mounted a old paint brush on the top of my saw that covers the blade. This keeps the spray under control and it allows me to use the saw without the blade cover.  The blade cover that comes with the saw makes it hard to see close work.  I also added a piece of plastic around the blade on the table (blackish square on the table) that allows for a zero or near zero clearance between the blade and table.  If you don't do that and want to cut small pieces of stones for jewelry,  then they can fall in the crack and sometimes jam the blade.  I also made a dike around the edge of the saw to contain the water so it doesn't drip off the sides, but rather into the slot. I used some plastic molding and just glued it to the table. 

The only think I have to do after each use is to make sure the tray under the blade is empty of water. If you leave water touching a typical diamond blade, it will rust in a matter of hours/days.  I use an aquarium tube to siphon the water into a jug. To start the siphon I don't suck on it, but rather use a syringe to pull the initial stream through the tube. Rocks contain all sorts of minerals that may be toxic, so I don't much like getting that slurry in my mouth!

The automatic feed mechanism is critical to the operation of the saw. As the motor dives the blade it can also drive a worm gear that pulls the rock toward the cutting action.  Some saws, like mine, have a separate motor to drive the worm gear.  The worm gear attaches to the rock vice with a "split nut."  This is an interesting mechanical device that clamps on the thread and pulls the vice forward.  To move the vice manually, you split that nut and disengage the threads.  Sometimes this mechanism wears out and needs to be rethreaded. I've done it once thus far in 10 years of use.