Its highly unlikely it will break from weight alone. Depending on the tank sometime the bottom pane is tempered glass which is even less likely to break.
is a video to ease your worries. Though I would question the title. That tank looks to be a standard 10 gallon, which don't actually use tempered glass... Only larger tanks like 55 gallons have tempered glass and its ONLY the bottom pane of glass. Tempered glass is also known as safety glass, same you find in your car. Its MUCH stronger then regular glass, but if it fails it fails entirely and turns into thousands of little pieces. Tempered glass cannot take any impacts to the edges, unlike regular glass. Which is why you rarely see fully tempered tanks, the common chip on a edge of a tank that doesn't effect its stability would fracture a tempered pane completely. Its also why you don't drill the bottoms of larger tanks unless you know they are not tempered(older tanks), or almost all of the time
Your 25 is most likely entirely made of regular glass, or just the bottom pane is tempered since it is a deeper tank. If you bought it new they usually have a sticker saying "tempered glass" stuck to the bottom if it is tempered. I know my 55 gallon does, its between the glass and the bottom center brace of the frame and can only be read if the tank is empty. Glass and silicone is a lot stronger then a lot of people realize. The plastic frame on a lot of smaller tanks is just for looks and owner safety, it doesn't impart any strength to the tank. Only on larger tanks does it protect the edges of the bottom tempered pane and the cross braces prevent bowing of the glass.
Also in regards to your question, its really the water not the rocks that give the weight in a normal aquarium. A 25 gallon weighs about 200 pounds just counting water. I'm guessing the weight of your substrate is much less then that. My 55 has a 2" deep substrate and that weights 100 pounds compared to the 440ish pounds of water it holds.