4. ppm

7. Minerals
Natural, inorganic, solid compounds with definite chemical composition and structure
Each mineral species = a unique pairing of a composition and a structure
Physical properties: color, hardness, crystal shape, cleavage (breaking along flat surfaces), density
Resource-important physical properties: hardness, strength, ductility, melting point, density, electrical conductivity, heat conductivity/insulation
Chemical properties: reactivity (including solubility), ability to combine with other materials, elemental composition
Resource-important chemical properties: weather- and chemical-resistance, which elements retrievable from the mineral, how much energy required to retrieve elements (how difficult to recover those elements), what undesired residues left after element recovery, what chemicals used in the recovery.

11. “environment”