3. The mineral zircon (ZrSi04) typically contains several hundred to several tho

Question

3. The mineral zircon (ZrSi04) typically contains several hundred to several thousand ppm U but much lower concentrations of Th. Explain why both statements are true. 4. Explain why quartz is typically > 99.9% pure SiO2 while other minerals contain significant concentrations of elements not in their formulas. 5. Explain why the color of many minerals can vary widely, but other properties, e.g., cleavage (or lack thereof) and hardness are much more consistent. 6. A mineral contains 63.5% Fe and 36.5% s. Derive the chemical formula for the mineral, using integer amounts of Fe and S. Show your work.

Explanation / Answer

4. Quartz is a part of the Tectosilicates which are also known as framework silicates because of thir three-dimensional network of Silica tetrahedra. The Si:O ratio is 1:2. All the 4 oxygen atoms of each tetrahedra are shared with other tetrahedra. Their exists a high covalent bond between Si and O. Besides, the whole structure is interlocking. Thus, they interact minimally with other ions and other ions cannot easily substitute in their three dimensional framework of silica tetrahedra.

In contrary, other minerals fall in the other group of silicates like nesosilicates, phyllosilicates, sorosilicates, cyclosilicates, chain silicates whose structures are such that they leave room for other atoms to substitute in place of original atoms. Besides, their Si:O ratios conform with the ability of the atoms to share other ions.

5. Colour of minerals can vary widely due to the property called dichroism or pleochroism. This is because colour is related to electromagnetic radiation and its interaction with the electrons of the elements. Electromagnetic radiation is a spectrum comprising a wide wavelength. However, cleavage is the inherent property of minerals and it is constant in a particular mineral. It cannot vary.

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