Feldspar is a blanket term for a very large group of minerals that are extremely abundant on Earth. Around 60% of the Earth's crust is made up of these minerals, in fact, and they have numerous uses for humans, ranging from scouring solutions to glassware. Chances are that most people are probably looking at something which contains feldspar right now, although they may not be aware of this, since these minerals are so ubiquitous in the industrial world. Globally, the major commercial sources are Italy, Turkey, China, and Thailand.
The distinguishing feature of minerals in the feldspar group is that they are comprised of silicates of aluminum blended with other metals like potassium, calcium, sodium, and sometimes barium. The composition of an individual piece determines its chemical properties and what color it will be, but it shares similarities with other feldspars, like a crystalline structure. Before feldspar can be used in an industrial process, it must be profiled to determine its chemical composition, as different types will of course behave differently.
Many feldspars are formed in magma, crystallizing out as the magma cools, making them igneous rock. It also appears in the form of veins in other rocks, formed through processes of pressure, classifying it as a metamorphic rock as well. Feldspar sometimes occurs in sedimentary rocks also. Regardless as to the process which led to their formation, feldspathic rocks contain blocky crystals.
In the Earth, one of feldspar's important roles is in clay formation; as the material weathers, it turns into clays. Humans use it in pottery and glassmaking, and it is also added to scouring powders and used as a filler in a wide range of products. Some are quite attractive, leading people to use them as semi-precious gemstones, as they can polish up quite nicely, and feldspar is also used to make decorative accents on buildings and monuments. It can also be used to date various materials, using a variety of techniques depending on the type of mineral involved.
Many natural history museums keep several excellent examples of various types of feldspar in an array of colors and sizes. Examining such a display can give people a good idea of the diversity of this mineral group, which appears in the ground we walk on, the glasses we drink from, and in a large array of other materials as well, ranging from tile grout to toilets.