About 4-1/2# of what appears to be 120 grit blasting media. Looking at it under a microscope, it's uniformly graded irregular waferish particles of about .005 long. That, the fact that it scratches glass aggressively, and the gray-brown color, make me think it's more likely silicon carbide than aluminum oxide. Or it could be something else entirely.
McMaster gets about $30 for 10# of AlO or SiC. If you want to gamble $10 thru Paypal for a Priority Mail flat rate box, it's yours. Otherwise, it goes into the driveway sand bucket.