Why does dolostone weather to a brownish colored rock?

W) Iron occurs in small amounts, replacing some of the magnesium in dolomite

X) Copper ions replace magnesium in dolostone as groundwater permeates the rock

Y) Aluminum ions replace the calcium in the dolomite compounds, and there is a reaction

between aluminum and the remaining magnesium ions

Z) Magnesium ions replace the calcium ions in dolostone compounds
W) IRON OCCURS IN SMALL AMOUNTS, REPLACING SOME OF THE