1) As Quartz has the formula Si02 does this mean that impurities are not part of the lattice structure? What I don't understand is how can it have the formula Si02 even though it is not completely pure. Ti, H20 or Fe can be found as trace elements yet they are not part of the formula. If we take Biotite for example it comprises several end members which are reflected in its formula. The same applies for Olivine (Fe,MgSi04). Why is quartz not shown as say (Fe,Ti,Sio2)?
2) Is quartz completely covalenty bonded becuase it is so strong?
2007-03-17 21:27:54 · 3 answers · asked by Gideon 1 in Science & Mathematics ➔ Chemistry
1 The impurities are not part of the lattice structure itself
2007-03-17 21:31:14 · answer #1 · answered by Anonymous · 0⤊ 1⤋
Quartz is an important mineral in igneous rocks and some metamorphic rocks. Igneous and metamorphic rocks were created by the intense pressure and heat of volcanic activity. Their impurities vary. When it is written (Si, Fe, O2), this refers to an igneous rock, of which quartz is an important part. Therefore, the formula does not reflect quartz, but a rock of which it is a part.
The impurities in quartz can be inclusions that don't necessarily combine with the quartz crystal lattice. They can simply be inclusions in the material not bonded to SiO2 tetrahedron.
In the case of olivine, the Mg and Fe are the two minerals that can fit into a certain site in the olivine lattice. The amount of Fe and Mg relative to each other is how we get eith Fayalite, which is the Fe rich endmenber and Forsterite, the Mg rich endmember. The Fe and Mg are built into the olivine. The impurities in quartz are not necessarily built in, but present along with. Thats why quartz has the same properties (shape, etc) but is just a different color.
It's called ionic substitution. Sometimes atoms of similar size and valency can be substituted within the crystal lattice. These impurity's can cause a slight change in colour or appearance. The amount of substitution can sometimes be noted in the chemical formula, but is often not due to there being more than one substitution taking place.
2007-03-22 15:36:15 · answer #2 · answered by Apolo 6 · 0⤊ 0⤋
The crystal systems are a grouping of crystal structures according to the axial
system used to describe their lattice. therefore I don't believe a impurity to be part of the crystal structure. and for answer number two ... yes and no because to have a covalent bond it requires more than just the quartz so that depends
2007-03-17 21:36:57 · answer #3 · answered by Kagen H 2 · 0⤊ 0⤋