Because these sulfides are much denser than the silicate minerals formed by lithophile elements, chalcophile elements separated below the lithophiles at the time of the first crystallisation of the Earth's crust.
12.
After dehydration, solute-rich fluids are released from the slab and metasomatise the overlying mantle wedge of MORB-like asthenosphere, enriching it with volatiles and large ion lithophile elements ( LILE ).
13.
Manganese, iron and molybdenum " do " form strong bonds with oxygen but in the free state ( as they existed on the primitive Earth when free oxygen did not exist ) can mix so easily with iron that they do not concentrate in the siliceous crust as do true lithophile elements.
14.
One group includes elements having large ionic radius, such as potassium, rubidium, caesium, strontium, barium ( called "'LILE "', or large-ion lithophile elements ), and the other group includes elements of large ionic valences ( or high charges ), such as zirconium, niobium, hafnium, rare earth elements ( REE ), thorium, uranium and tantalum ( called "'HFSE "', or high field strength elements ).
