Iron is used for the frame of automobiles and reacts with oxygen in the air to produce rust. Magnesium is used in flares. Calcium is a major component in our teeth and bones. Sodium is in table salt. Potassium is used in fertilizer.
Titanium is combined with other metals to produce alloys, which are stronger metals.
Plagioclase is a common mineral in many volcanic rocks. Photo by Steve Mattox. It must be inorganic. It must be a solid element or compound. It must have a definite composition.