Stone makes for a very poor shovel material. It doesn't stand up well to prying or levering without snapping, a wide flat blade would be hell to knap, and unlike in an axe it's mass is of no benefit. In fact the extra mass is a liability in a shovel- you have to swing it around without it helping the shovel's function in any way. And the advantage of flint for knives, spears, arrows, etc. was sharpness, which also doesn't help a shovel very much. Well, except for some tasks some cultures reinforced a wooden shovel's blade with stone chips to make it sharper, like for peat cutting, but that is the closest there ever was to a practical stone shovel, and even then bone was more common.
There were certainly stone adzes and hoes. But historically, primitive shovels were either wood or bone (bone shovels usually being made from an animal scapula)- well into the iron age, as a matter of fact. Stone shovels are essentially absent from the archaeological record, other than maybe some ceremonial objects.