Earth crust is the source of many elements . Out of these elements , 70 % are metals . Aluminium is the most abundant metal of earth crust and iron comes second . The percentage of different elements in earth crust are
O-49 %, Si-26 %, Al-7.5 %, Fe-4.2 %, Ca-3.2 %, Na-2.4 %, K-2.3 %, Mg-2.3 %, H-l %
Metals occur in two forms in nature ( i ) in native state ( ii ) in combined state , depending upon their chemical reactivities .
Native State
Elements which have low chemical reactivity or noble metals having least electropositive character are not attacked by oxygen . moisture and CO2 of the air . These elements , therefore , occur in the free state or in the native state , e . g ., Au , Ag , Pt , S , O , N , noble gases , etc .
Combined State
Highly reactive elements such as F , CI , Na , K , etc ., occur in nature combined form as their compounds such as oxides , carbonates sulphides . halides , etc .
Hydrogen is the only non-metal which exists in oxidised form only .
Minerals and Ores
The naturally occurring substances in the form of which the metals occur in the earth crust are called minerals .
Every mineral is not suitable for the extraction of the metal . The mineral from which the metal is economically and conveniently extracted is called an ore .
Thus , all ores are minerals but all minerals are not ores .