Grandreefite is a rare secondary

lead sulfate Lead(II) sulfate (PbSO4) is a white solid, which appears white in microcrystalline form. It is also known as ''fast white'', ''milk white'', ''sulfuric acid lead salt'' or ''anglesite''. It is often seen in the plates/electrodes of car batteries, ...

fluoride Fluoride (). According to this source, is a possible pronunciation in British English. is an inorganic, monatomic anion of fluorine, with the chemical formula (also written ), whose salts are typically white or colorless. Fluoride salts typ ...

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ( ...

with a general chemical formula, Pb₂SO₄F₂. It is named for the location in which it was discovered in 1989, the Grand Reef Mine in

Graham County, Arizona Graham County is a county in the southeastern part of the U.S. state of Arizona. As of the 2020 census, the population was 38,533, making it the third-least populous county in Arizona. The county seat is Safford. Graham County composes the ...

. Grandreefite is

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic s ...

, falling in the 2/m symmetry group. Crystallographically this means, grandreefite has three axes of unequal length, with two angles at 90° to one another and a third, obtuse angle. The 2/m symmetry group indicates a two-fold axis with a perpendicular mirror plane. Grandreefite was originally classified as an

orthorhombic In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a r ...

mineral but was determined monoclinic instead upon further analysis. Pseudograndreefite, one of three other newly discovered minerals in 1989 at the Grand Reef Mine site, has orthorhombic crystallography. Optically, grandreefite is an anisotropic mineral, meaning the velocity of light varies depending on the direction through which it is passing through the mineral. Its calculated relief, i.e. its relative difference in index of refraction compared to the surrounding medium's index of refraction, is 1.96–1.98; and its birefringence is .025. Grandreefite, while not a valuable mineral in terms of commercial use, is useful in the sense that it is a good indicator of the very specific environment in which it forms and therefore the same conditions required to produce minerals similar to it in structure, composition, etc. For example, its structure is very similar to that of

lanthanide The lanthanide () or lanthanoid () series of chemical elements comprises the 15 metallic chemical elements with atomic numbers 57–71, from lanthanum through lutetium. These elements, along with the chemically similar elements scandium and yttr ...

oxide sulfates and therefore may be used to help better describe them. The Grand Reef Mine is located near a large

granitic A granitoid is a generic term for a diverse category of coarse-grained igneous rocks that consist predominantly of quartz, plagioclase, and alkali feldspar. Granitoids range from plagioclase-rich tonalites to alkali-rich syenites and from quart ...

intrusion In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

. Grandreefite is usually found in the mine in isolated

veins Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated b ...

containing

hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...

silver Silver is a chemical element with the Symbol (chemistry), symbol Ag (from the Latin ', derived from the Proto-Indo-European wikt:Reconstruction:Proto-Indo-European/h₂erǵ-, ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, whi ...

, and

lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...

minerals hosted in

oxidized Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of di ...

References

{{Reflist * Kampf, A.R. (1991) Grandreefite, Pb₂SO₄F₂;Crystal Structure and relationship to the lanthanide oxide sulfates, Ln₂O₂SO₄. American Mineralogist, 76, 278-282. * Kampf, A.R., Dunn P.J., and Foord E.E. (1989) Grandreefite, pseudograndreefite, laurelite, and aravaipaite: Four new minerals from the Grand Reef Mine, Graham County, Arizona. American Mineralogist, 74, 927-933. Lead minerals Sulfate minerals Monoclinic minerals Minerals in space group 15