This term is a "category" for the EWG Framework
Definition as it applies to our work: Feedstock is the first of three stages of material production. Included in this part of the materials supply chain is the growing or mining of the material in question.
Examples
Oil is the feedstock to make polyester granulate
Cotton Farming is the feedstock raw cotton fiber
How about "earth to granulate or raw fibre". This would encompass farming practices or a polymerization process. Coverting the granulate or natural fibre into a useable material or substrate would then be "Raw Materials Stage".