rockwool

plural rockwools · alternative rock wool

1. countableuncountableInorganic material resembling fiber, used primarily for insulation and soundproofing.
2. countableuncountableA horticultural growing medium made from natural ingredients, usually including basalt rock and chalk.

   In 1985, rockwool was introduced to the United States as an alternative to conventional soil and other soilless mediums. Rockwool is made of thin fibers of volcanic rock or a combination of volcanic rock, limestone, and coke.

   1997, George F. Van Patten, Alyssa F. Bust, Gardening Indoors with Cuttings