Why marbles don't shatter like a glass panel does? Both are made of the same material, not talking about the tempered glass. But I don't see marbles shatter the way glass panel does, why is that? If I could scale up the marble to the size of a car and strike a hammer on it, would it shatter?
 A: The difference is geometry, both in shape and size.
First, consider that the smaller something is, the stiffer it is in general. Take a large rubber eraser and squeeze it (in compression,  not bending) and then cut it in half and squeeze again. You need double the force to get the same deflection with half the size.
Next is the shape, where something flat like a glass pane is allowed to bend which puts the most strain into the material, compared to a sphere that mostly compresses. The details here are complex, but certain shapes are stiffer and certain ones are more complaint. A sphere is exceptional at resisting loading because most of the internal stresses are compressive.
Brittle shattering occurs when the bonds between molecules in a solid break (in tension) causing a dislocation, which then loads up neighboring molecules which in turn break also. In the end, there is a runaway process of crack propagation until the object is fully cracked.
A: Let me try again and answer the actual question that was asked.
I am not a material scientist but I do know that glass is a brittle material and fracture by the propagation of crack.
This is more likely to happen if the glass is in a state of tension rather than in a state of compression.
Depending on how the marbles are manufactured on possible explanation is that as the marbles cool the surface solidifies whilst the centre is still molten.
As the cooling process continues the centre solidifies whilst at the same time contracting thus closing up cracks at the surface and so reducing the chances of fracture.
I think this is not the explanation as when a marble does break I have not noticed it breaking explosively into many pieces as happens to a toughened car windscreen.
The video cited by @JohnAlexiou shows marbles shattered by the application of lerge compressive forces using a hydraulic press.
Another video Smashing A Marble Into Pieces with a Hammer!! shows how difficult it is to break a marble with a hammer but it also points to a possible answer to the question.
At approximately [3:30] in the video a larger marble is used but more significantly placed on what looks like a concrete surface where the previous attempts seem to be made on a softer surface.
This time the marble fractured.
So perhaps having two hard surfaces (the hammer head and the concrete floor) distorts a marble enough to open up some cracks which will then cause the marble to fracture.
With the hydraulic press this is done in a more controlled fashion and the compressed marble with a store of spring potential energy fractures explosively as that energy is released.
Just dropping a marble does not cause enough distortion to allow cracks to form and propagate and hence for fracturing to occur.
Further investigation lead me to How to Make Cracked Marbles where factures in the glass are achieved by quenching a hot marble in cold water.
What is interesting is that although numerous cracks are formed within the glass a lot of the time the marble stays as a whole showing that the cracks which are formed are not on the whole "joined up".
Overall I think that to break a glass marble it has to be distorted by quite a degree for it to fracture whereas with a pane of glass any distortion is likely to put one side of the glass under tension and hence make a fracture more likely.
