Cut-polished facets of illustrious minerals shine with captivating beauty. These minerals are commonly touted as gifts to be cherished for generations. However, there is a mineral that could be equally if not more important than their companion minerals, like quartz.
Known as feldspars, these minerals are not only important to the function of our planet but they are also known for bonding strongly with water molecules.
Rock-Forming Minerals
Feldspar refers to a group of naturally occurring alumino-silicate minerals that contain varying amounts of sodium, potassium, calcium, and lithium. It is by far the most abundant mineral group in the crust of the Earth, making up about 50% of all rocks. Their fine particles can also be found in the atmosphere.
Because of their atomic structure, feldspars can be found in different shapes and colors. They are abundant because the elements, pressure, and temperature within the magma and melts favor their formation.
Feldspar can be pretty generous and include many other elements left over during the formation of the parent rock. At the surface of the Earth, these minerals are no longer stable and begin to weather away. As a result, they release plant nutrients and form important secondary clay minerals.
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Why Is Feldspars Always Wet?
Water molecules bond to the surface of the minerals, and in the case of a potassium-rich subset of feldspar, ice nucleation happens much faster than it does with other minerals. Potassium feldspar is an important part of cloud formation, yet water molecules prefer to bond with this mineral remains a mystery.
This has been the focus of two studies conducted by the Technical University of Vienna and Bielefeld University in Germany. Led respectively by Ulrike Diebold and Angelika Kühnle, the investigations focused on examining the atomic surface of potassium feldspar.
In this research, the researchers used an ultra-high vacuum to break the mineral along the natural break or cleavage plane, allowing them to get a flat, dry surface. When they looked at the sample, it was already wet. It was found that the water released by small pockets in the mineral during breaking had already bonded with the alternating silicon and aluminum atoms on the surface of the potassium feldspar.
The result of the study "Atomic structure and water arrangement on K-feldspar microcline (001)" was not an experimental failure. The property of the dry surface to instantly become hydroxylated matched with what happens in nature.
It was discovered that potassium feldspar is always wet because it bonds immediately with water in the air. Since the surface atomic structure of this mineral is made of alternating aluminum and silicon ions, the water on the surface of the mineral forms a regular pattern of hydroxyl groups. Then, the first layer of dissociated water molecules helps the additional layers of water bond to the surface quickly.
Evidence also shows that ice nucleation can happen around potassium feldspar at higher temperatures than it can around water. This could be partly due to the structure of hydroxyl groups in the first water layer.
Seeing the atomic structure of potassium feldspar experimentally is only a first step for atmospheric scientists. There is still work to be done to understand why potassium feldspar facilitates cloud formation better than other minerals.
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