Hi,
Please explain how its classified - Is it a material type / material group / material classification characteristic or class. Please explain.
If its material classification, then you may proceed as explained by Mr. Jurgen
If its a material type / material group, you can get the list from MM60 transaction.
If its based on any other fields in material master, you may get the list from table or using an SQVI querry.
Regards,
AKPT