what needs to be scratched to measure hardness?
nails stoma air h2o oaks poles weater gems
A B C D E F G H
Most gem stones are hard minerals.
measuring gem hardness requires scratching them
what needs to be scratched to measure hardness? (A) nails (B) stoma (C) air (D) h2o (E) oaks (F) poles (G) weater (H) gems