Geo-Chemestry

**Back Ground information:

Zircon group are simple tetragonal silicates,

Zircon (ZrSiO4) is a common accessory mineral in nature, occurring in a wide variety of sedimentary, igneous and metamorphic rocks.

"Describe the structure of your mineral group"

The structure for the Zircon group is Tetragonal, classic example of how this structure works is the mineral Zircon which as stated above is tetragonal and crystallizes in space group I41/amd. Both Zr4+ and Si4+ cations occupy special positions with site symmetry 4–2m. The O atom occupies a site with symmetry m: The y and z coordinates of the O atom are the only refinable atomic-site parameters in the zircon structure [y = 0.066, z = 0.195]

In the above diagram we see that the principal structure is a chain of altering edge sharing SiO4 tetrahedra and ZrO8 triangular dodechedra extending parallel to "c",

And also the chains are joined laterally by edge-sharing

What known species occur in Nature with this structure?

Actinide silicates – There are three naturally occurring ATO4 actinide silicates two of which are isostructual with zircon = Coffinite (USio4) and Thorite (ThSio4)

Phosphates - Three naturally occurring REE phosphates = xenotime (YPO4), xenotime-(Yb) (YbPO4) and pretulite (ScPO4) which all crystallize with the zircon structure

Borates - Two naturally occurring borates are known that possess the zircon structure, both of which share the general formula (Ta,Nb)BO4.

Also Scheelite (CaWO4), Monazite (CePO4), Rutile (TiO2), Garnet (X3Y2T3O12),