It would weigh about 14.3 pounds .
Granite weighs an average of about 20 pounds per square foot, so a 5' by 8' (40 square feet) piece of granite would weigh approximately 800 pounds.
About 18# per sq ft
with only length and width it cannot be determined.
Just short of 11,000 pounds roughly. Average density of granite is about 2.7 g/cm3.
Most weigh around 42 lbs. They must be between 38 and 44 lbs per World Curling Federation rules.
They both weigh a kilogram.
The quartz content of granite is varied.
As much as 1% in granites sold for interior use. That is "granite" not granite though.