Before you start…
Be sure to observe the stone from every angle to comprehend its volume. There are two options when choosing a size and shape, Either your project is well established in terms of dimensions and you choose a bigger block that you will rough-hew to find your chosen shape, or you observe the rough natural shape of the stone and imagine what creation could come out of it. The latter is probably more interesting from an artistic point of view.
Observe the veins that mark the stone as they are decisive for the choice of tools because they can easily crack open during sculpting. You can also wet the stone initially to get a sense of the true colour when finishing and how your finished piece will look.
If you wish to divide your block in two, you can use a handsaw which offers a clear cut. To obtain several blocks, you can use a sledgehammer and a chisel. Breaking the stone rather than sawing helps to avoid breaks or nasty surprises whilst shaping as the stone will break on the places that were already weakened by the small cracks inherent in the stone. You will obtain the same result by dropping the stone on a hard floor. Keep the stone splinters; you will be able to make small objects or jewels with them.
Rough-hewing the block
Before starting, sketch your intended shape onto the stone with a pencil, then start to progressively rough-hew your stone, first with the saw and then a file or saw rasp as the shape starts to form. Do not think about the final result yet but think about the general shape of what you want to create. The hewing step is doubtlessly the longest and most delicate step. It is therefore imperative to take your time, observe the progression of the work, and allow yourself to take a break and stand back in order to comprehend the shape
Unlike a painting, a sculpture will be observed from every angle. So make sure you take the time to manipulate your block and turn around it during the work to observe its full effect. If it is a large block, its helps to also stand back from time to time to get a better point of view.
Defining the Shape
All the tools used for working with wood can be used: rasp, files etc … you can also use a chisel, metal drills, or a saw. But to let your imagination run free and sculpt complex details and shapes, it is recommended to use rifflers. These tools of diverse shapes and sizes are especially designed for precise work. The mixed rifflers (two different points) are very interesting for this step because they allow the artist to use different techniques without changing his tools. The piriform rifflers for example allow you to create cavities of all shapes and depths and needle or bird tongue rifflers will help you define small details.Think about all aspects of the shape, including the base which can be improved by refining with the rifflers.
In order to maintain your tools use a wire brush when finished to eliminate the stone dust.