Cause of Death Still an Official Mystery

9/17 -- We've obtained Mac's death certificate which lists his official time of death as 11:51 AM PT on the morning of September 7. His occupation was listed as musician for 11 years. Mac will be buried at The Homewood Cemetery in Pittsburgh.

Mac Miller's cause of death is still officially unknown ... according to his death certificate.

TMZ's learned the doc, filed with L.A. County, notes the cause of death is "deferred" ... meaning the L.A. County Coroner is awaiting toxicology results.

The point of a death certificate with a deferred cause of death ... so the family can either bury or cremate the body. We've learned the Coroner has already released the body to Mac's family.

The toxicology results typically take 4 to 6 weeks.

TMZ broke the story ... the rapper was found dead of an apparent overdose last week in a bedroom at his San Fernando Valley home. He was pronounced dead at the scene.

Authorities were alerted by a friend who called 911 from Mac's home. Emergency dispatch audio revealed first responders were called for a patient in cardiac arrest.

As we first reported ... cops think Mac's house was swept clean before cops searched it for clues as to how Mac died. Our sources say it makes no sense to them that someone who had consumed a fatal dose would have the foresight to sweep the house of pill bottles, illegal drugs as well as drug paraphernalia on the off chance they might die.