3) When zircon (ZrSiO.) crystallizes from a magma, it commonly admits U4 into it

Question

3) When zircon (ZrSiO.) crystallizes from a magma, it commonly admits U4 into its crystal structure, but strongly excludes Pb. Deduce the valence of Pb in magma from this observation. Show your reasoning. The two main types of meteorites found on Earth are the iron and the stony What exactly are meteorites, where do they come from, and what do these two types tell us about the composition of the Earth? 4) 5) In each of the following pairs, choose the one in which the chemical bond would have more covalent character a) KCl and KI b) Li,S and Cs,S c) BaCl, and HgCl d) KCl and BaC e Cu,O and Cu2S

Explanation / Answer

3)When ZrSiO4 crystallises from magma it incorporates trace elements which could replace its Zr site of +4 . U has +4 charge and hence will be suitable to be incorporated into the crystal .The crystal strogly displaces Pb because it has a charge of +2 and to stabilize the negetive charge in ZrSiO4 the +2 charge would not be a stable configuration .

4) The stony and iron meteorites are commonly found on earth. First of all meteorites are extraterrestrial bodies of differentiated or un differentiated bodies formed by collapse of planetesimals . As most planetesimals are composed of irons in core and silicates on the outer part hence it can suggest the earth compositions to be of combinations of silicate and iron . We can suggest a heterogeneous model of formation of earth by this process . The meteorites come from the asteroid belt between mars and jupiter and this belt is thought to be the threshold for the volatile matter presence in the inner planets . Hence can be suggested that earth is mostly composed of iron and silicates.

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