atomic number 3, Li, lithium - a soft silver-white univalent element of the alkali metal group; the lightest metal known; occurs in several minerals

atomic number 37, Rb, rubidium - a soft silvery metallic element of the alkali metal group; burns in air and reacts violently in water; occurs in carnallite and lepidolite and pollucite

isinglass, mica - any of various minerals consisting of hydrous silicates of aluminum or potassium etc. that crystallize in forms that allow perfect cleavage into very thin leaves; used as dielectrics because of their resistance to electricity