Streak plates are used to identify what kind of mineral is being used. The little square plates are made out of unglazed porcelain. You can take a mineral and scratch it against the tile to see what kind of mark it makes.
SIUE STEM Resource Center
http://www.siuestemcenter.org/
Southern Illinois University Edwardsvillehttp://www.siuestemcenter.org/
Science East, Room 1276
Edwardsville, IL, 62026
USA
618-650-3065