User:Klm10/sandbox

Context Memo: I chose to edit this article ebcasue it was listed as a top importance start on the Geology WikiProject. The weathering section specifically was only one sentence, and it's a topic I've learned about in class many times so I know it fairly well and thought I could confidently expand on it. My addition is an important aspect of a very important mineral (the most common in Earth's crust). I added mostly information I've learned in classes and that I re-found in textbooks or articles.

Chemical weathering of feldspars happens by hydrolysis and produces clay minerals, including illite, smectite, and kaolinite. Hydrolysis of feldspars begins with the feldspar dissolving in water, which happens best in acidic or basic solutions and less well in neutral ones. The speed at which feldspars are weathered is controlled by how quickly they are dissolved. Dissolved feldspar reacts with H+ or OH- ions and precipitates clays. The reaction also produces new ions in solution, with the variety of ion controlled by the type of feldspar reacting.

The abundance of feldspars in the Earth's crust means that clays are very abundant weathering products. About 40% of minerals in sedimentary rocks are clays, and clays are the dominant minerals in the most common sedimentary rocks, mudrocks. They are also an important component of soils. Feldspar that has been replaced by clay looks chalky compared to more crystalline and glassy unweathered feldspar grains.

Feldspars, especially plagioclase feldspars, are not very stable at the earth's surface due to their high formation temperature. This lack of stability is why feldspars are easily weathered to clays. Because of this tendency to weather easily, feldspars are usually not prevalent in sedimentary rocks. Sedimentary rocks that contain large amounts of feldspar indicate that the sediment did not undergo much chemical weathering before being buried. This means it was probably transported a short distance in cold and/or dry conditions that didn't promote weathering, and that it was quickly buried by other sediment. Sandstones with large amounts of feldspar are called arkoses.