Estimated of 80 elements are obtained from mineral deposits on or beneath the surface of the earth.

• Metals which are sufficiently unreactive to occur uncombined (i.e. in elementary form) are present in group 10 and 11 of the 2nd and 3rd transition series (e.g. Pt, Au, Ag; free Ag is also found in nature).
• Metalloids (e.g Ge, As, Sb) and neighbouring metals, all of which have relatively large ionization energies, generally occur as
• The more strongly metallic elements that form positive ions readily are found as oxides (transition metals), carbonates (group 2 metals) or chlorides (group 1 metals).
  • Three noble metals (Cu, Ag, Au), Hg and six platinum metals (Ru, Os, Rh, Ir, Pd and Pt) occur in nature in free state. All other metals are found in combined state in the nature.
  • The composition of earth’s crust is: O (49.1%), Si (26%), Al (7.5%), Fe(4.2%),  Ca (3.2%),  Na  (2.4%),  Mg (2.3%)  and H (1.0%) by weight.
  • In combined state metals are found as (a) Oxides – Mg, Cu, Zn, Al, Mn, Fe, etc. (b) Carbonates – Na, Cu, Mg, Ca, Ba, Zn, Fe etc. (c) Phosphates – Ca, Pb, Fe etc (d) Silicates– Li, Cu, Zn, Al, Mn, Ni, etc and  (e) Sulphates – Fe, Cu, Pb, Hg etc.

Sources from Sea

Four elements such as Na, Mg, Cl2 and Br2 can be extracted from the oceans or salt brines, where they are present as monoatomic ions (Na+, Mg2+, Cl-, Br -).

Source from living system

Below table indicates descending mass abundance of elements. About 30 percent of enzymes have a metal atom at the active site. A large number of biomolecules contain metal ions ; many of these molecules are proteins. In addition metal ions in the form of crystalline minerals or amorphous solids are important as structural materials in many organisms.

Descending mass abundance of the elements

Earth	Oceans	Humans
Crust
O	O	H
Si	H	O
Al	Cl	C
Fe	Na	N
Ca	Mg	Na
Mg	S	K
Na	Ca	Ca
K	K	Mg
Ti	C	P
H	Br	S
P	B	Cl