Potassium Feldspar

This is the mineral Potassium Feldspar. It is also called K-Feldspar, because K is Potassium’s symbol on the Periodic Table. You may also hear it called Orthoclase Feldspar, or simply Orthoclase. It’s one of Earth’s most abundant rock-forming minerals. Like most other rock-forming minerals, it belongs to the Silicate chemical family because it contains repeating chains of linked Silicon and Oxygen tetrahedra. In addition to its Silicon and Oxygen components, the mineral also contains Potassium and Aluminum. It typically exhibits a vitreous, or glassy, luster, and produces a white streak when drawn across a streak plate. Potassium Feldspar defines Mohs hardness rank number 6. Note that most renditions of Mohs hardness scale simply list it as Orthoclase. It has two well-defined cleavage planes that meet at right angles. With a specific gravity of 2.6, it feels neither especially heavy nor especially light in your hand. Note that Potassium Feldspar is part of a large group of minerals collectively referred to as Feldspars. This group also contains a mineral called Plagioclase Feldspar, often simply called Plagioclase. The two minerals have many similar physical characteristics, but they differ in their chemical composition. While Potassium Feldspar contains the element Potassium, this element is replaced by either Sodium or Calcium in Plagioclase Feldspar. As a result of this elemental difference, Potassium Feldspar often appears pink or salmon-colored, while Plagioclase Feldspar often appears grey or white. Note that there are always exceptions to this color differentiation. Recall that both minerals are rock-forming Silicates, and both are commonly seen in the rock called Granite. Granite is an intrusive igneous rock typically exhibiting large crystals due to its slow cooling deep inside Earth’s crust. If some of the large crystals in a sample of Granite appear pink or salmon-colored, they are likely Potassium Feldspar. If they appear white or grey, they are likely Plagioclase Feldspar. Note that Granite will also be composed of the mineral Quartz, and likely contain Amphibole, Biotite, and or Muscovite. We commonly use Potassium Feldspar as aggregate when producing concrete and asphalt. Aggregates are simply coarsely crushed rocks and minerals. Potassium feldspar is also used to manufacture glass, glaze ceramics and metals in enamel, and create scouring powder. When the mineral weathers, its Potassium, Silicon, and Oxygen dissolve away, leaving behind significant Aluminum deposits. When Aluminum is concentrated in sedimentary rock, that rock is called Bauxite. Bauxite is a critical ore for Aluminum. Consider, therefore, how you’re connected to the mineral Potassium Feldspar the next time you open an Aluminum can, use Aluminum foil, or even fly on an airplane.

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