whether it makes any diffrence if we use glass ?
I do not agree with the assumption in your question, as the mineralogy of a weathered rock depends on its pre-weathering mineralogy. If you take, for example, a weathered limestone, dunite, or basalt, you are not going to find any quartz or K-spar. If you take a weathered sandstone (very difficult to weather), you are not going to find any k-spar. That is because the mineral you are looking for did not exist in the first place. Quartz is very resistant to weathering (see Bowen's Reaction Series or Goldich Weathering Series). It is hard and chemically resistant, and that is the reason beaches and river gravels are composed dominantly of quartz. K-spar (also called potassium feldspar, potash feldspar, or more correctly orthoclase feldspar) is not a resistant mineral, as it weathers to clay minerals by hydrolysis according to this formula: 2KAlSi3O8 + 3H20 --> Al2Si2O5(OH)4 + 4SiO2 + 2K(OH) .
