Firestone apparently died of natural causes Tuesday at her apartment in the East Village of Manhattan, The New York Times reported.
Firestone's 1970 book, subtitled "The Case for Feminist Revolution," made waves for its bold claims that reproduction should be separate from sex and that conception and gestation should take place outside the body in an artificial womb. She cited Marxists theories to support her thesis.
"Just as the end goal of socialist revolution was not only the elimination of the economic class privilege but of the economic class distinction itself," Firestone wrote, "so the end goal of feminist revolution must be ... not just the elimination of male privilege but of the sex distinction itself: Genital differences between human beings would no longer matter culturally."
The overwhelming attention -- positive and negative -- she received for the book caused her to retreat from public life, spending most of her time painting and writing, her sister, Laya Firestone Seghi said.
Firestone wrote one other book, "Airless Spaces" in 1998, about her hospitalization in the 1980s for schizophrenia.