These wafers are made of 99.9999% pure silicon (Si, 14) and were used to manufacture computing components (the namesake of Silicon Valley). Memory, processors, sensors, microcontrollers or other components are etched into the silicon and laser cut from the wafer before being put to work. However, these were not cut and instead pull from production while still intact. They now make for gorgeous display pieces, extremely pure silicon samples for element collectors, or teaching aides for computing students.
Note: The wafer you receive may have a similar but slightly different pattern