Does a brand of Johns Manville Spintex rock wool insulation from the years 1950 have any asbestos?

Rock wool is a product manufactured by melting rock and rock-like materials and forming it into thin fibers, roughly similar to the manufacturing of fibreglass. A product that is truly rock wool cannot contain asbestos because even if asbestos had been present in the raw materials, which was not the case, it would have been destroyed in the manufacturing process.

However, the only way to know with certainty today whether something identified as 1950s era rock wool really is rock wool and not asbestos is to have a sample collected and analysed by qualified people and laboratories.