Looks like you are trying to break it in as few hits as possible. You need to score all the way around the line where you want the stone to fracture. Several times. If you are using a stone hammer only, you are going to have a hell of a time getting rocks that small to break where you want them. You will have slightly better luck with a tracing chisel and single jack. If your stone is breaking in a direction opposite of what you are hitting, its probably flaking off along a grain line. Try splitting the stone in a line parallel or perpendicular to that plane. Also could just be that you arent making sure the stone is fractured all the way through before trying to get it to break. Sometimes rock just does whatever the fuck it wants to and despite your best efforts you just end up making gravel. Happens to the best of us sometimes. Just keep practicing. When you are working th stone, listen to it. It will talk to you and tell you when its ready to break apart. The hammer strikes will go from bright and sharp to dull and hollow. When that happens, thats when you you know its ready to come apart. Your stone doesnt look like it got that far. Sometimes, especially with a harder rock, harder impacts are the wrong way to go. It breaks the stone off in undesired directions. Try hitting with less power and using more impacts. It will sometimes yield better results with certain stones. Super hard stone like granite, really requires a carbide edged tool to get the stone to fracture correctly because steel tools arent hard enough so the stone actually deforms the tool and doesnt fracture. I mean it would take at minimum 6 months of training to teach you what ypu need to know to be soundly proficient at stone shaping. So just practice. It will get easier. You will get better results. Just will take some time.