Two keys, one for minerals and one for rocks, briefly present clues that may aid the collector in identifying rocks and minerals found in Illinois. In outline form, the keys are a guide to some of the easily observable properties that various rocks and minerals display. The rocks and minerals in the school set of “Typical Rocks and Minerals of Illinois” are included, plus other relatively common ones you might find in Illinois. Because of the great diversity of rocks and minerals in this state, the keys are not conclusive. It is therefore suggested you consult other more complete keys (such as that in Dana’s _Manual of Mineralogy_) when identifying rocks and minerals that are either from other states or are difficult to identify. The minerals (p. 30-35) are arranged in two groups: 1) those with a metallic luster, and 2) those with a nonmetallic luster. Each group is arranged according to increasing hardness. Other characteristics such as color, streak, cleavage, fracture, and composition are listed. The rocks (p. 36-39) are arranged according to their reaction to dilute hydrochloric acid applied to a scratched surface. (The acid reacts more readily to powdered material produced by scratching the rock.) After the reaction to acid has been determined, the texture and components of the rock should be noted. Because rocks grade into one another, clear distinctions are not always possible. MINERAL IDENTIFICATION KEY I. METALLIC LUSTER, STREAK COLORED C—color H—hardness Remarks Name and S—streak Cl—cleavage composition F—fracture A. Hardness not more than 2.5 C—lead gray H—2.5 Very heavy; occurs as Galena (31) S—black Cl—cubic; crystals, grains, or PbS perfect in 3 masses; easily directions identified by color and F—subconchoidal cleavage or even C—copper red H—2.5 Very heavy; apt to have Native copper S—metallic, Cl—none green coating; distorted Cu shiny F—jagged or wirelike forms; malleable B. Hardness greater than 2.5 but not greater than 6.5