greenspun.com : LUSENET : Introductory Geology, Oswego State : One Thread

In class Monday we talked about Hydrolysis. I was wondering why potassium feldspar leaves a solid of clay minerals and doesn't dissolve completely like a calcite mineral would.

-- Sandra Feocco (DOMINICK F @ Prodigy.NET), February 27, 2001


I found this information on the internet in Encarta.msn.com under Calcite. I hope this helps a little. Calcite group - Group of minerals belonging to the carbonate group that are isomorphous with one another and have the same properties. Minerals in this group can partially or fully replace one another. For example, iron may take the place of magnesium in Magnesite Calcite is only slightly soluble in pure cold water. However, rainwater or other water in contact with air will absorb carbon dioxide from the air. Carbon dioxide reacts with water to form carbonic acid. Calcite reacts with carbonic acid to form calcium bicarbonate. Calcium bicarbonate is quite soluble in water. Thus, the solubility of calcite is sensitive to the acidity of the water. The solubility of calcite is also sensitive to the temperature of the water, being quite soluble in hot water but not in cold water. Calcite frequently dissolves in one location and precipitates in another location when the water becomes less acidic or cools.

(MgCO3), transforming it to Siderite (FeCO3). This information was found in the Encyclopedia under Potassium. Potassium is found in nature in large quantities, ranking eighth in order of abundance of the elements in the crust of the earth, in various minerals such as carnallite, feldspar, saltpeter, greensand, and sylvite. Potassium is a constituent of all plant and animal tissue as well as a vital constituent of fertile soil.

My guess is that because calcite is a dissolvable and potassium feldspar is a mettalic which is undissolvable are the reasons you are looking for. I hope I am right or on the right track for you.

-- Tina Miller (sultice@aol.com), February 27, 2001.

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