I. Title Calcite Family II. Introduction Trivia - One of the most common minerals on Earth, calcite forms many rock types including limestone, marble, and travertine. It can also be found in caves as stalagmites and stalactites. Calcite is the main component in the shells of sea creatures. As they die and fall to the seabed more rocks rich in calcium are created. Calcite - is a mineral that forms rocks and has the chemical formula CaCO3. It is extremely common and can be found in sedimentary, metamorphic, and igneous rocks worldwide. Some geologists consider it a 'ubiquitous mineral,' as it can be found anywhere. - is an abundant mineral found in many geological environments. It forms by precipitation from ground and surface waters, forming the major component of marl and limestone in the ocean, lakes, and rivers. It also forms speleothems in caves, euhedral crystals in bugs, and tufa where springs emerge on the surface. III. What is Calcite? - Calcite is a mineral that forms rocks and has the chemical formula CaCO3. It is extremely common and can be found in sedimentary, metamorphic, and igneous rocks worldwide. Some geologists consider it an 'ubiquitous mineral,' as it can be found anywhere. Calcite is the main component of limestone and marble. These rocks are extremely common and account for a huge percentage of the Earth's crust. They are one of the world's largest carbon repositories. IV. Crystal Structure - Calcite is an abundant mineral found in many geological environments. It forms by precipitation from ground and surface waters, forming the major component of marls and limestone in the ocean, lakes and rivers. It also forms speleothemes in caves, euhedral crystals in vugs, and tufa where springs emerge on the surface. It is the major component of marbles, which forms by the metamorphism of limestones and other carbonate-rich rocks. Calcite also is commonly found in hydrothermal veins. It may occur as a rare accessory in syenitic or pegmatitic igneous rocks. Space allows only a few of the most remarkable calcite occurrences to be mentioned here. Most of the state’s calcite occurrences are in a region underlain by Paleozoic carbonate rocks, which extend in a wide curving band across the state from St. Croix County in the west, south along the Mississippi Valley east to Madison, then north to Green Bay and the Door Peninsula. V. Physical properties - The diagnostic properties of calcite include a defining Mohs hardness of 3, a specific gravity of 2.71, and, in crystalline varieties, a vitreous luster. Color is white or none, though shades of gray, red, orange, yellow, green, blue, violet, brown, or even black can occur when the mineral is charged with impurities. The structure of calcite—one of the first mineral structures to be determined by X-ray methods—has been described on three different bases. The two most frequently used bases, illustrated in Figure 1, are the true rhombohedral unit cell, which is the acute rhombohedron, and the cleavage rhombohedron setup. Calcite has perfect cleavage in three directions to produce rhombohedra. VI. Occurrence - Occurrence of Calcite occurs in major rock-forming minerals; in limestones, marbles, and chalks; a common cement in clastic sedimentary rocks; as gangue in hydrothermal veins; in alkalic to mafic igneous rocks; and commonly as speleothems in caves. It is the main mineral found in metamorphic marble. It can also be found as a vein mineral in hot spring deposits, stalactites and stalagmites in caverns, volcanic or mantle-derived rocks such as carbonatites, kimberlites, and rarer cases, peridotites. VII. Varieties of Calcite Optical Calcite Optical calcite or Iceland spar is a transparent variety of calcite known for its remarkable optical properties. It exhibits strong birefringence, causing double refraction of light. This property made it historically important in navigation and as a tool for understanding the polarization of light. Iceland spar is also used in scientific demonstrations and educational settings. Dogtooth Calcite Dogtooth calcite, also known as nail head spar, is characterized by its scalenohedral crystal habit, resembling dog’s teeth or nail heads. It often forms in cavities and fractures of rocks and can occur in a range of colors. Dogtooth calcite crystals can be quite large and impressive, making them desirable for collectors. Mangano Calcite This variety of calcite contains significant amounts of manganese, which can give it a pink to reddish color. Mangano calcite is often associated with other manganese-rich minerals and can be found in various geological settings. Cobaltoan Calcite Cobaltoan calcite is a pink to-purple variety containing cobalt. It’s valued for its vibrant color and is commonly associated with other cobalt-bearing minerals. It’s often found in oxidized ore deposits. Honey Calcite Honey calcite is a variety with a golden to honey-yellow color. It’s often found as coatings on other minerals or in sedimentary rock layers. Its warm color makes it a popular choice for lapidary use and as a decorative stone. Calcite Twinning Calcite can exhibit various types of twinning, where two or more individual crystals grow together in specific orientations. One of the most famous twinning patterns is the “Roman Sword” twin, characterized by two calcite crystals crossing each other at a specific angle. VIII. Uses of Calcite 1. Construction and Building Materials: Limestone: Calcite is a major component of limestone, a common construction material used for buildings, roads, and monuments. Limestone’s durability, workability, and aesthetic qualities make it a favored choice in construction. 2. Agriculture and Soil Enhancement: Calcium Source: Calcite is added to agricultural soils as a source of calcium, an essential nutrient for plant growth. It also helps to regulate soil pH, improving nutrient availability to plants. 3. Decorative Objects and Gemstones: Ornamental Use: Highly transparent calcite crystals are sometimes used as decorative objects and even as gemstones. These crystals can be faceted and polished to showcase their optical properties. 4. Dietary Supplements and Pharmaceuticals Calcium Supplements: Calcite is a natural source of calcium, and calcium carbonate derived from calcite is used in dietary supplements and antacids to provide calcium to the body. IX. Calcite in Geology X. Conclusion XI. References Mat, M. (2023). Calcite. Geology Science. https://geologyscience.com/minerals/calcite/?amp Calcite. (2021, April 2). WGNHS. https://home.wgnhs.wisc.edu/minerals/calcite/ https://www.mordorintelligence.com/industry-reports/calcite-market
