Sentence:  In 1985, <WSD>rockwool</WSD> was introduced to the United States as an alternative to conventional soil and other soilless mediums. <WSD>Rockwool</WSD> is made of thin fibers of volcanic rock or a combination of volcanic rock, limestone, and coke. 
Meaning of the word marked with <WSD> tags:  A horticultural growing medium made from natural ingredients, usually including basalt rock and chalk.