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Maricite

Abstract
The mineral maricite, NaFePO4, is a sodium iron phosphate that has two metal cations connected to a phosphate tetrahedron. It is very structurally similar to the much more common mineral LiFePO4, because they both have a phosphate anion. The differences are that LiFePO4 has lithium instead of sodium and the two minerals have different coordination aside from their phosphate anion. Maricite is brittle, usually colorless to gray, and has been found in nodules within shale beds often containing other minerals. Maricite is most commonly known to be found in the Big Fish River area of the Yukon Territory, Canada, but it has also been found in Eastern Germany, as well as inside of various meteorites around the world. Maricite is named after Dr. Luka Maric of Croatia, (1899-1979), the long time head of the mineralogy and petrography departments at the University of Zagreb. Maricite is of scientific interest right now because it has been found as a hideout reaction product which has caused corrosion problems in the boilers of fossil-fired electrical power generating stations. Also, because there is a growing interest in the production of sodium ion batteries, scientists are taking a closer look at maricite because it is a sodium ionic compound.

Introduction
Maricite is a sodium iron phosphate from the extremely diverse phosphate mineral group. In 1977 maricite was discovered in the Big Fish River area, Yukon Territory, Canada (Fleischer, Chao, and Mandarino, 1979). This is an important geologic location that has provided the discovery of several phosphate minerals which have been previously unknown. Maricite is recognized for its possible use in sodium ion battery research as well as its role as a reaction product inside of fossil-fired electrical power generating station boilers which experience corrosion (Bridson, et. al, 1997; Ong, et. al, 2011).

Composition
Maricite is a member of the phosphate mineral group. Phosphate minerals have one or more metal cations bonded to the phosphate anion PO4. (Hawthorne, F.C., 1998). In maricite the metals bonded to PO4 are sodium and iron (Sturman, et. al, 1977). The empirical formula for maricite is NaFePO4 and it has a molar mass of 173.81 g/mol (Yahia, et. al, 2008; Tremaine, Xiao, 1999). The general formula for maricite is ABPO4, (Yahia, et. al, 2008). The chemical composition was originally found by Dr. Corlett from the Department of Geological Sciences at Queen’s University, Kingston, Ontario. The formula was determined using electron microprobe analysis, and the resulting formula was found to be, Na0.91(Fe0.89Mn0.07Mg0.03)P1.02O4.00 (Sturman, et. al, 1977) when normalized to four oxygen atoms. The weight percentages were determined using six different points on a thin section and averaging the percentages of each oxide in all of the samples. The results in weight percent average of oxides are as follows: Na2O 16.5%, MgO 0.8%, CaO 0.0%, MnO 3.1%, FeO	37.4%, P2O5 42.5%, with a total of 100.3%. When looking at these results, one may determine that the majority of the oxide weight composition is made of FeO with P2O5 making up almost the same weight percentage. There is a significant percentage of the Na2O oxide and an insignificant percentage of the CaO oxide (~0). It is clear from looking at the oxide content of the mineral that the main components are going to be sodium, iron, phosphorous, and oxygen. The oxide factor may be used to determine the weight percentages of the individual elements as follows, 1 sodium atom totaling ~13% of composition, 1 iron atom totaling ~32% of composition, 1 phosphorous atom totaling ~18% of composition, and 4 oxygen atoms totaling ~37% of composition (Sturman, et. al, 1977).

Structure
Maricite is an ionic double metal phosphate, with a space filling capacity of about 70% (Le Page, and Donnay, 1977). The structure of maricite contains a sodium cation enclosed by ten oxygen anions within 10 Å, in an irregular coordination. There is (2+2+2) type distorted tetrahedron around the iron (Bridson, et. al, 1997). The Å distances between iron and oxygen are between 2.33-2.93. The phosphate tetrahedron is almost regular, with 2 short bonds and 2 longer bonds (Bridson, et. al, 1997). The iron atom has four surrounding oxygen atoms giving it tetrahedral coordination. Half of the oxygen atoms are coordinated with two sodium atoms, two iron atoms, and one phosphorous atom while the other half are coordinated with three sodium atoms, one iron atom and one phosphorous atom (Bridson, et. al, 1997). The structure of maricite has been compared to the structure of olivine, LiFePO4, (Lee, et. al, 2011). The structures of the two minerals are similar because they both contain PO4 in their atomic make-up (Moreau, et. al, 2010). However, the M1 and M2 sites for LiFePO4 and NaFePO4 have reverse occupancies making their structures different (Lee, et. al, 2011). In olivine, the M1 site holds the alkali metal while the M2 site holds the transition metal, whereas in maricite, the M1 site holds the transition metal and the M2 site holds the alkali metal (Ong, et. al, 2011). Due to the differences in the M1 and M2 sites for maricite, the Fe and Na octahedral is connected to the phosphate tetrahedron differently, making its structure unlike the structure of olivine (Lee, et. al, 2011). In the olivine (LiFePO4 ) structure, each phosphorous atom is surrounded by four oxygen atoms in tetrahedral coordination making it very similar to the maricite structure. The structure of LiFePO4 is different from NaFePO4 because the A element in the general formula ABPO4 is lithium instead of sodium. Also, the lithium atom is surrounded by six oxygen atoms in octahedral coordination, while the sodium atom in maricite is surrounded by ten oxygen atoms in an irregular coordination. Also while the B element in both LiFePO4 and NaFePO4 is iron, the iron atoms do not have the same coordination. In the olivine structure, the iron atom is surrounded by six oxygen atoms in octahedral coordination, while in the maricite structure the iron atom is surrounded by four oxygen atoms in tetrahedral coordination. However, while the coordination of the iron atom is different in the two structures, the Fe-O distances are about the same, 2.1567 Å for LiFePO4 and 2.185 Å for NaFePO4 (Lee, et. al, 2011; Moreau, et. al, 2010).

Physical Properties
Maricite (NaFePO4), is found in elongated grains up to 15 cm long in the [100] direction. The grains are radial to sub parallel in structure. Maricite is usually colorless to gray, but is sometimes a pale brown color and it has a white streak. It has a vitreous luster due to its low values of refractive indices, α = 1.676 β = 1.695 γ = 1.698, and its opacity is transparent to translucent (Fleisher, et. al, 1979). Maricite has no cleavage or pleochroism, and it does not fluoresce in UV light. Maricite has a hardness of 4-4.5 and a density of 3.64. The mineral is brittle, with an uneven splintery fracture. It is a member of the orthorhombic crystal class and the biaxial negative optical class and has a 2V calculation of 43°. The Hermann-Mauguin notation symbol is 2/m 2/m 2/m, and it is in the Pmnb space group. Yvon Le Page and Gabrielle Donnay determined that the cell dimensions are a 6.864(2), b 8.994(2), and c 5.049(1). J. A. Mandarino determined the d-spacings using x-ray powder diffraction and Bragg’s law to be 2.574 at an intensity of 100, 2.729 at an intensity of 90, 2.707 at an intensity of 80, 1.853 at an intensity of 60, 3.705 at an intensity of 40, 2.525 at an intensity of 30, and 1.881 also at an intensity of 30 (Fleisher, et. al, 1979; Sturman, et. al, 1977).

Geologic Occurrence
Maricite was first discovered in the Big Fish River area near the eastern border of the Yukon territory around Latitude 68° 30’ N and Longitude 136° 30’ W. This area is a kulanite-baricite-peniksite type locality composed mostly of embedded shales and sideritic limestones. Maricite has been found in nodules up to 15 cm long inside of the shale beds. Some of the nodules contained only one mineral, while others contained several different minerals. Very few of the nodules consisted of only maricite. Most of the samples which contained maricite also had quartz, ludlamite, vivianite, pyrite, and/or wolfeite. When samples which appeared to only contain maricite were examined closely in a thin section, there were small inclusions of ludlamite, quartz, and vivianite present along the fractures (Sturman, et. al, 1977). The other location which formations of maricite have been found is Saxony Germany (Thomas, R. and Webster J.D., 2000). Both this location and the Big Fish River Canada location are situated just north of convergent plate boundaries. Both areas consist of mountains and hills which are made of metamorphic and igneous rocks (Thomas, R. and Webster J.D., 2000; Sturman, et. al, 1977). Maricite has also been discovered in meteorites found in Eastern Antarctica, Uttar Pradesh, India, and Avanna Province Greenland (Johnson, et. al, 2001; Kracher, et. al, 1977; Partridge, et. al, 1990).

Who in the World
Maricite was named by Darko Sturman and Joseph Mandarino in honor of Dr. Luka Maric. Dr. Maric was the long time head of the department of mineralogy and petrography at the University of Zagreb in Croatia. The name Maricite was approved in 1977 by the commission on new minerals and mineral names. It is unclear exactly why the mineral was named in honor of Dr. Maric, but he did author several geology books including one entitled Magmatiti u Uzhem Podruchju Rudnika Bor u Istochnoj Srbiji‎, which is Croatian for Magmatites in the Narrower Ore Deposit Region of the Bor Mine (Sturman, et. al, 1977).

Literature Survey and Prospects for Further Investigation
The Synthesis and Crystal Structure of Maricite and Sodium Iron (111) Hydroxyphosphate by John N. Bridson, Sean E. Quinlan, and Peter R. Tremaine is the most cited article about maricite describing how maricite and sodium iron (111) phosphate may be synthesized in a lab by thermally decomposing the complex of iron (111) nitirilotriacetic acid at 200°C. This research on maricite synthesis has been done because sodium phosphate hideout (the principle hideout reaction product being maricite) has caused corrosion problems in the boilers of fossil-fired electrical power generating stations due to usage of low concentrations of sodium phosphate to control the pH of the boiler water. This has only been the case for some stations, while others have also used phosphate water treatments, and have no occurrence of corrosion. Additional research of maricite could be useful in determining what is causing corrosion in the boilers of certain electrical power generating stations while not in others (Bridson, et. al, 1997). The second most cited information directly related to maricite is a journal article written in 1977 by Le Page and Donnay titled The Crystal Structure of the New Mineral Maricite NaFePO4. This article contains a detailed description of the crystal structure of maricite. Modern society is quickly growing dependent upon lithium ion batteries for digital devices and portable electronics. During the 1970’s, research began on both sodium ion batteries and lithium ion batteries, and due to the success of lithium ion batteries, research on sodium ion batteries has been of less importance. However, due to the abundance of sodium in comparison to lithium, sodium ion batteries could prove to be a less costly alternative to lithium ion batteries (Ong, et. al, 2011). Maricite could be very useful in studying sodium ion batteries because it a sodium ionic compound.