7. Calcite
Calcite, or calcium carbonate, is one of the most common minerals on earth. It can be found in large, sedimentary rock masses and in limestone. It can also be found in cave deposits, such as stalactites, stalagmites, and incrustations. Since it is so common, it is nearly impossible to specify every occurrence of calcite; h owever, there are a few well-studied localities where calcite crystals can be found. These localities include the Harz Mountains, Germany; Lancashire, England; Joplin, Missouri; and Guanajuato, Mexico.
Depending on where calcite is found, it can range in color from yellow to colorless. There have been some specimens found where the mineral was tinted green, blue, gray, and even red. If it is brown or black in color, it is considered to be impure.
The luster of calcite also varies from vitreous or glass-like to resinous. When found in large masses, it can even appear dull. In addition, since finger can easily scratch it, it is not considered a hard mineral.
Calcite crystals often enclose quartz sand. The combination of the crystals and the quartz sand create sandstone crystals. These crystals are most prominent in Fontainebleau, France, and in the Badlands of South Dakota.
There are several different uses for calcite. The most important use is for the manufacture of cement and lime for creating mortar. Limestone is the main raw material; however, when it is heated, it forms quicklime. When the calcite from the limestone is mixed with water, it sets and makes mortar.
8. Feldspar
Feldspar is a blanket term for a very large group of minerals which are extremely abundant on Earth. Around 60% of the Earth's crust is made up of feldspar, in fact, and these minerals have numerous uses for humans, ranging from scouring solutions to glassware. Chances are that you are probably looking at something which contains feldspar right now, although you may not be aware of this, since these minerals are so ubiquitous in the industrial world. Globally, the major sources of commercial feldspar 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 of feldspar 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 feldspars will of course behave differently.
Many feldspars are formed in magma, crystallizing out as the magma cools, making feldspar an igneous rock. Feldspar 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 the formation of feldspar, 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 feldspar in pottery and glassmaking, and it is also added to scouring powders and used as a filler in a wide range of products. Some feldspars 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. Feldspar can also be used to date various materials, using a variety of techniques depending on the type of feldspar 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 you 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.
In the Earth, one of feldspar's important roles is in clay formation; as the material weathers, it turns into clays. Humans use feldspar in pottery and glassmaking, and it is also added to scouring powders and used as a filler in a wide range of products. Some feldspars 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. Feldspar can also be used to date various materials, using a variety of techniques depending on the type of feldspar 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 you 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.
