strontium

a soft silver-white or yellowish metallic element of the alkali metal group; turns yellow in air; occurs in celestite and strontianite

A metallic element of the calcium group, always naturally occurring combined, as in the minerals strontianite, celestite, etc. It is isolated as a yellowish metal, somewhat malleable but harder than calcium. It is chiefly employed (as in the nitrate) to color pyrotechnic flames red. Symbol Sr. Atomic weight 87.3.