A dark variety of sandstone, much used for building purposes.
A row housebuilt of brownstone; reddish brown in color.
A reddish brown sandstone; used in buildings.
He was in the West Nineties, a long block of brownstone rooming houses.
(William S. Burroughs, 'The Junky's Christmas')
Means Heroin and is also a famous song by Guns N Roses on their debut album "Appetite for Destruction". When they are saying "Dancing with Mr. Brownstone" it means they are "Shootin Heroin"
"We Been Dancin' with Mr. Brownstone
He's been knockin he won't leave me alone"