CompuServe Messages

Kamron: <<what is missing is segregations of the material that was with the original sand materials. These missing components…>> What about all that mud…and all the salt in the oceans? I don't think there is any "missing" material that needs to be explained away. The ultimate origin of all clastic sedimentary rocks is igneous and metamorphic rocks–granites, lavas, gneisses, etc. All these primary rocks are composed of mixtures of minerals, some of which are less resistant to chemical and mechanical weathering than others. For example, granite is made up of feldspars (mostly), quartz and dark minerals such as micas. Feldspar and mica are broken down by chemical weathering processes–mildly acidic rain water, organic compounds–to produce clay minerals (such as kaolinite) and ions (such as potassium and magnesium). The clay minerals are concentrated to form clays and muds, while the ions wind up in the sea to form various salts. What's left? Quartz! Quartz is relatively resistant to both chemical and mechanical weathering, so ends up being concentrated as sand. The hardest and most inert minerals in any rock are likely to be concentrated as sand under the right conditions, including garnet (a common component of schists) and magnetite (common in many volcanic rocks).