6 weeks ago I purchased an allegedly tempered glass, 40x66x1/2" rectangular table top with rope (shell) edge. It had previously been on table in a furniture store show room and appeared to be in perfect condition there. I placed it on a 16"X48" rectangular pedestal base for the first couple of week and transferred it to its present 22.5"X44" oval, rattan base 16 days ago. The crack is in the overhang that extends 11.5 inches from the end of the base (The opposite overhang is slighly less).
A 7" crack was discovered today. Loading on the overhang was limited to a 6.4 lb, 11"x13" lap top computer. For the past couple of days, the computer had been in the center of the longitudinal overhang. The crack veered slightly towards the adjacent edge. Sometime later I discovered that an extension of the crack had occurred, taking off at an angle towards the center of the nearest end of the support.
The greatest loading stress this overhang would have experienced in the past would have been from a a 13.5"x19" loaded tray that may have weighed 11 pounds. There has been no impact stress or heat stress.
I would like to know whether the above mentioned conditions are likely from:
1. a manufacturing defect
2. the loading mentioned above, or
3. another cause. Please explain
Thank you for your advice.