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Home , Brazilianite, Phosphate mineral

PHYSICAL PROPERTIES:

Chemistry: NaAl3(PO4)2(OH)4 Basic Aluminum , often containing traces of iron. Class: , Arsenates, and Vanadates Subclass: Basic Anhydrous Phosphates Group: Brazilianite System: Monoclinic Crystal Habits: Usually short prismatic, spearhead-shaped ; also spherical- drusy, massive, globular, and radial-fibrous forms. Color: Usually yellow and greenish-yellow to yellowish-green and chartreuse-green; occasionally colorless; colored varieties can appear colorless when viewed with transmitted light. Luster: Vitreous Transparency: Transparent to sub-transparent : White : Good in one direction : Conchoidal, brittle. Hardness: 5.5 Specific Gravity: 2.9 Luminescence: None : 1.602-1.623 Distinctive Features and Tests: Best field identification marks are color, hardness, and occurrence in phosphate-rich, in association with such as [sodium aluminum silicate, NaAlSi3O8], [mica group, basic potassium aluminum silicate, KAl3Si3O10(OH)2], elbaite[ group, basic sodium aluminum lithium borosilicate, Na(Al1.5Li1.5)Al6(BO3)3(Si6O18)(OH)4], and -CaF [calcium fluorophosphate, Ca5(PO4)3F]. Brazilianite is sometimes confused with [beryllium aluminum oxide, BeAl2O4] and yellow varieties of [basic aluminum fluorosilicate, Al2SiO4(F,OH)2], both of which are harder. Dana Classification Number: 41.5.7.1

NAME: The name “brazilianite,” pronounced bruh-ZILL-yun-ite, stems from , the nation where the was discovered. In European mineralogical literature, brazilianite appears as Brazilianit, brazilianita, and brasilianite.

COMPOSITION: Brazilianite’s chemical formula NaAl3(PO4)2(OH)4 shows that it consists of five elements: sodium (Na), aluminum (Al), phosphorus (P), oxygen (O), and hydrogen (H). Brazilianite’s molecular weight is made up of 6.35 percent sodium, 22.37 percent aluminum, 17.12 percent phosphorus, 53.05 percent oxygen, and 1.11 percent hydrogen. The brazilianite molecule, like all molecules, is composed of positively charged cations and negatively charged anions. Brazilianite’s compound cation consists of one sodium Na1+ with its +1 charge and three aluminum 3Al3+ with their +9 charge. Together, these ions produce a collective,

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cationic +10 charge. The brazilianite anion consists of two radicals (groups of ions of different 3- atoms that behave as single entities in chemical reactions). These are the phosphate ion (PO4) 1- 3- and the hydroxyl ion (OH) . Brazilianite’s three phosphate radicals 3(PO4) provide a -6 charge, while its four hydroxyl ions 4(OH)1- contribute a -4 charge. This collective -10 anionic charge balances the +10 cationic charge to provide the brazilianite molecule with electrical stability.

As a phosphate, brazilianite is one of more than 300 members of the phosphates, arsenates, and vanadates class of minerals. The basic building blocks of these minerals are the phosphate 3- 3- 3- radical (PO4) , the arsenate radical (AsO4) , and the vanadate radical (VO4) . All form tetrahedral structures with four oxygen ions surrounding the ion of a metal or semi-metal (vanadium is a metal, arsenic and phosphorus are semi-metals). In the phosphate radical, the phosphorus ion P5+ is surrounded by and bonded covalently to four oxygen ions 4O2-. The resulting collective -3 charge, which is distributed evenly over the four oxygen ions, enables the phosphate radical to bond ionically to different metal cations.

In brazilianite, two phosphate radicals bond ionically to one sodium and three aluminum ions to 4+ form the intermediate, octahedral-shaped, sodium aluminum phosphate radical [NaAl3(PO4)2] . These radicals, which are unstable because of their +4 charge, bond together into chains of octahedra that establish brazilianite’s monoclinic . In spaces between these linked octahedra, four hydroxyl ions 4(OH)1- bond ionically to alternating metal ions to complete the molecule and provide electrical balance. Monoclinic crystals have three axes of different lengths, two of which are perpendicular. The third axis is not perpendicular to the plane of the other two, but makes an angle that causes the crystals to appear to be orthorhombic with one- directional deformation. Compounds with complex chemistries or bonding arrangements often crystallize in the monoclinic system. The weak ionic bonding that predominates along a single plane accounts for brazilianite’s good, one-directional cleavage. Brazilianite’s hardness of Mohs 5.5 is due to close atomic packing that strengthens its atomic bonding. Despite its close atomic packing, brazilianite has only a moderate density (specific gravity 2.9) because of the light atomic weights of its elemental components. Aluminum (atomic weight only 26.98), the heaviest essential element in brazilianite, comprises just 22.37 percent of its total molecular weight.

The Dana mineral-classification number 41.5.7.1 first identifies brazilianite as an anhydrous phosphate, arsenate, or vanadate containing hydroxyl or halogen ions (41). The subclassification (5) defines it by the general formula (AB)2(XO4)Zq, in which “A” and “B” are a variety of metals; “X” is phosphorus, arsenic, or vanadium, “Z” is either hydroxyl or halogen ions, and “q” is a quantitative designator. Brazilianite is then assigned to the brazilianite group (7) as the first and only member (1).

Minerals are generally classified as allochromatic or idiochromatic according to the origin of their colors. The colors of idiochromatic or “self-colored” minerals are caused by essential elements or the light-absorbing properties of the crystal lattice. The colors of allochromatic or “other-colored” minerals are due to the trace presence of accessory elements called chromophores (color-causing agents). Brazilianite is allochromatic. When pure or nearly pure, it is colorless. Its characteristic yellow or yellowish-green to greenish-yellow or chartreuse- green colors are due to traces of the non-essential element iron, which distorts the crystal lattice, 2

causing it to absorb the blue and red ends of the white-light spectrum and to reflect only the yellow and green wavelengths.

Brazilianite occurs almost exclusively in phosphate-rich, granite pegmatites. Pegmatites, which are bodies of very coarse-grained granite, form when residual magma—the last magma to solidify—retains its heat and cools very slowly. Rather than quickly “freezing” into fine-grained granite, residual magma crystallizes on a fractional, or mineral-by-mineral, basis to form pods, lenses, pockets, and irregular dikes. As residual magma, which is often enriched with accessory or rare minerals, slowly solidifies, gases can create vugs or mariolitic cavities that provide space for the growth of unusually large, well-developed crystals. Gem-quality crystals of brazilianite form only in phosphate-rich, granite pegmatites in association with muscovite, albite, elbaite, and apatite-CaF [calcium fluorophosphate, Ca5(PO4)3F]. Very small amounts of massive brazilianite are also found in certain metamorphic rocks.

COLLECTING LOCALITIES: Although brazilianite is rare, it is distributed worldwide. Gem-quality brazilianite is extremely rare and found only in Brazil. The primary source is the Doce Valley in state near Davino das Laranjeiras and Linópolis where mines include the Córrego Frio (brazilianite type locality), Ellas Lopez, Almerindo, Fazenda Pomarolli, João Lopes, Pamaró, Tellrio, and Sebastião Cristino. Other Doce Valley sources are the Gentil and João Modesto dos Santos mines near Mendes Pimentel. Brazilianite also occurs at the Alto Patrimônio Mine at Pedro Lavrada in Paraiba state; and in the Altodo Giz at Equador and the Boqueirão pegmatite at Parelhas, both in Rio Grande do Norte state.

Non-gem-quality brazilianite occurs in the El Quemado district, Nevados de Palermo, Salta, ; the Yichun Mine in the Yashan Batholith, Yuanzhou District, Yichun Prefecture, Jiangxi Province, ; the Beauvoir Quarry at Allir, Auvergne, ; the Etiro pegmatite in the Karibib District, Erongo Region, Namibia; the Rubindi and Buranga pegmatites in the Gatumba District, Western Province, ; the Hagendorf South pegmatite at Vohenstrauss, Upper Palantinate, Bavaria, Germany; and the Teso de la Calera pegmatite at Zamora, Castile and Leon, Spain.

The primary sources of brazilianite in the United States, all in New Hampshire, include the Charles Davis, Fletcher, Nancy, and Palermo No. 1 mines at Groton in Grafton County; the Chickering Mine at Walpole in Cheshire County; and the G. E. Smith Mine at Newport in Sullivan County. Maine specimens come from the Bell Pit at Newry in Oxford County. Connecticut sources include the Fillow Quarry at Branchville in Fairfield County and the Strickland Pegmatite at Collins Hill in Middlesex County. Brazilianite also occurs at the Dan Patch Mine in the Keystone district, Pennington County, South Dakota.

JEWELRY & DECORATIVE USES: Transparent brazilianite is a valuable gemstone because of its unusual yellow-green colors. Although the apatite-CaF is occasionally faceted into collectors’ gems, brazilianite is the only major phosphate gemstone. It is usually faceted in square, emerald, or fancy cuts. With its refractive index of 1.602-1.623, equal roughly to that of topaz and the [beryllium aluminum silicate, Be3Al2Si6O18] gemstones, properly cut brazilianite gems have an eye-catching brilliance. But because of their brittleness and relative softness (Mohs 5.5), they ae usually worn only as pendants. With its good, one-

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directional cleavage, Brazilianite is difficult to cut. Most brazilianite gems contain visible inclusions and other flaws that make polishing difficult. Multi-directional polishing is usually necessary to achieve a high polish. Fine brazilianite gems are very costly and are often mounted in gold. Prices vary from $100 to nearly $1,000 per carat depending upon color, brilliance, freedom from flaws, and gem size. The most desirable brazilianite color is a distinctive, mid- range green-yellow that is greener than chrysoberyl, but more chartreuse-green than peridot [forsterite, magnesium silicate, Mg2SiO4]. Because brazilianite can occur in large crystals, gems weighing more than 100 carats have been cut and are displayed in museums. Few brazilianite gems are available on the gem markets for two reasons. First, gem-quality brazilianite itself is rare. Second, collector demand for crystal specimens is so high that little gem-quality brazilianite is actually cut. Brazilianite is one of the few minerals in which specimen value is often determined by carat weight.

Top-grade brazilianite crystals, obtainable from only a few Brazilian pegmatite mines, are among the most sought-after of all mineral specimens. Brazilianite is collected both as individual crystals and as composite specimens in association with muscovite, , elbaite, and albite.

HISTORY & LORE: Brazilianite is the most recently discovered major gemstone. Before the discovery of brazilianite in 1943, the last major gemstone to be discovered was benitoite [barium titanium silicate, BaTiSi3O9] in southern California in 1912. The discovery of brazilianite was due in part to the extraordinary events related to World War II. In 1942, Dr. Frederick Harvey Pough (1906-2008), who went on to become the best known American mineralogist and mineralogical author of his time, was ordered to Brazil as a field mineralogist as part of the wartime Manhattan Project. Pough’s mission was to find strategic sources of quartz and elbaite. The quartz had to be crystallographically perfect rock crystal for electronic applications; the elbaite had to have a high chemical purity for piezoelectrical uses.

Always on the lookout for unusual minerals, Pough inspected a dealer’s selection of “chrysoberyl” from the Córrego Frio Mine near the towns of Davino das Laranjeiras and Linópolis in the Doce Valley in Minas Gerais state. He noted their chrysoberyl-like color, but also recognized a different crystal structure and determined their hardness to be well below that of chrysoberyl. Pough purchased several of the crystals and sent them to Dr. Edward Porter Henderson (American mineralogist, 1898-1992) at the Smithsonian Institution in Washington, D.C. Henderson’s qualitative analysis of the specimens showed that they were not chrysoberyl at all, but an entirely new mineral species. In 1945, Pough and Henderson published the first formal description of the new mineral and proposed the name ‘brazilianite” in honor of Brazil. The type specimens, those used in Henderson’s conclusive analyses, remain in the Smithsonian collection.

For decades, brazilianite from Minas Gerais had been mistaken for chrysoberyl. But now that brazilianite was described, it took only two years for mineralogists to find another source—the pegmatite quarries of Grafton County, New Hampshire. Although other sources were later found, none yielded specimens comparable in crystal development, transparency, or overall gem quality to those of Brazil. Recognition of brazilianite as a new species spurred many museum curators and prominent collectors to test their prized “chrysoberyl” specimens. Many turned out to be much more valuable brazilianite.

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TECHNOLOGICAL USES: Brazilianite has no technological uses.

Celestial Earth Minerals www.celestialearthminerals.com Steve Voynick (C) copyright Celestial Earth Minerals

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