Cyrilovite
Encyclopedia
Cyrilovite is a hydrous sodium iron phosphate mineral. It is isomorphous and isostructural with wardite
, the sodium aluminium counterpart.
Cyrilovite is found in granitic pegmatite
s. It was first discovered in 1953 in a pegmatite at Cyrilov, near Velké Meźiřiči, West Moravia
, Czech Republic
.
Parent phosphate minerals, fluorapatite
and triplite
-zwieselite, were transformed by hydrothermal alteration and weathering
to give a complex, microcrystalline
intergrowth of secondary phosphate minerals that include cyrilovite. The sequence of phosphate transformations ended with the formation of cyrilovite within the fluorapatite fractures and the replacement of fluorapatite by lipscombite
and crandallite-group minerals. Fransolet suggest that a part of the leached Na leads to the precipitation
of cyrilovite, in the fissures cause by the volume decrease resulting from the transformation of typhylite to heteresoite. Mobilization of alkalis and of relatively immobile elements including aluminium and rare earth element
s are subsequently incorporated into precipitating cyrilovite, lipscombite and crandallite-group minerals.
The chemical analysis shows substitution not only of Al for Fe, but also of K and Mn for Na, measured and observed specific gravities
are considered to be in good agreement. Ferric
iron occurs virtually alone in H20 rich minerals such as phosphosiderite, and coupled with Na, K, or Ca in cyrilovite. It is soluble in hot dilute HCl
, in hot dilute H2SO4
, and, with difficulty, in hot dilute HNO3
. In the closed tube, it gives off water and fuses.
The mineral wardite is capable of crystallizing in a similar form to that of cyrilovite because of their closely related chemical compositions. Between wardite’s composition, NaAl3(PO4)2(OH)4•2(H2O), and cyrilovite’s composition, NaFe3(PO4)2(OH)4•2(H2O), they’re able to form end members of a series of solid solutions. Either of the two minerals can occur in various proportions in a series of solid solutions in the wardite mineral group. Cyrilovite is a rare accessory mineral in some oxidizing phosphate-bearing granite pegmatitles and iron deposits. The sequence of phosphate transformations ended with the formation of cyrilovite within the F-apatite factures and the replacement of F-apatite by lipscombite and crandillite-group minerals. Weathering related cyrilovite, lipscombite, and crandillite-group minerals were formed by percolating meteoric waters under increasing oxygen fugacity
.
The crystal structures of natural wardite and of the isomorphous cyrilovite have the space group
P41212, Z=4). Hydrogen atoms were not located, but reasonable positions can be estimated. The cell dimentsions of cyrilovite are: c=19.4, a=7.32 Å
.
The individual crystals are usually smaller than 0.1 mm and many of them are intergrown. Crystals are squat and when single tend to lie on the basal pinacoid. The pinacoid {001} and the dipyramid {113} are the dominant forms; all the faces of thse forms tend to be present and equally well developed. The dipyramid {012} is not always present. The direction for the a-axis is at 45° angle to the smallest primitive unit cell.
Wardite
Wardite is a hydrous sodium aluminium phosphate hydroxide mineral with formula: NaAl324·2. Wardite is of interest for its rare crystallography. It crystallizes in the tetragonal trapezohedral class and is one of only a few minerals in that class. Wardite forms vitreous green to bluish green to...
, the sodium aluminium counterpart.
Cyrilovite is found in granitic pegmatite
Pegmatite
A pegmatite is a very crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size; such rocks are referred to as pegmatitic....
s. It was first discovered in 1953 in a pegmatite at Cyrilov, near Velké Meźiřiči, West Moravia
Moravia
Moravia is a historical region in Central Europe in the east of the Czech Republic, and one of the former Czech lands, together with Bohemia and Silesia. It takes its name from the Morava River which rises in the northwest of the region...
, Czech Republic
Czech Republic
The Czech Republic is a landlocked country in Central Europe. The country is bordered by Poland to the northeast, Slovakia to the east, Austria to the south, and Germany to the west and northwest....
.
Composition
The chemical formula of cyrilovite is NaFe3+3(PO4)2(OH)4•2(H2O).Parent phosphate minerals, fluorapatite
Fluorapatite
Fluorapatite, often with the alternate spelling of fluoroapatite, is a mineral with the formula Ca53F . Fluorapatite is a hard crystalline solid. Although samples can have various color , the pure mineral is colorless as expected for a material lacking transition metals...
and triplite
Triplite
Triplite is a rare phosphate mineral with formula: . It occurs in phosphate-rich granitic pegmatites typically as irregular brown opaque masses. Triplite was first described in 1813 for an occurrence in Chanteloube, Limousin, France. The name is from the Greek triplos for triple, in reference to...
-zwieselite, were transformed by hydrothermal alteration and weathering
Weathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...
to give a complex, microcrystalline
Microcrystalline
A microcrystalline material is a crystallized substance or rock that contains small crystals visible only through microscopic examination.-See also:* Macrocrystalline* Microcrystalline silicon* Protocrystalline* Rock microstructure...
intergrowth of secondary phosphate minerals that include cyrilovite. The sequence of phosphate transformations ended with the formation of cyrilovite within the fluorapatite fractures and the replacement of fluorapatite by lipscombite
Lipscombite
Lipscombite 222 is a green gray, olive green, or black. phosphate-based mineral containing iron, magnesium, and iron phosphate....
and crandallite-group minerals. Fransolet suggest that a part of the leached Na leads to the precipitation
Precipitation (chemistry)
Precipitation is the formation of a solid in a solution or inside anothersolid during a chemical reaction or by diffusion in a solid. When the reaction occurs in a liquid, the solid formed is called the precipitate, or when compacted by a centrifuge, a pellet. The liquid remaining above the solid...
of cyrilovite, in the fissures cause by the volume decrease resulting from the transformation of typhylite to heteresoite. Mobilization of alkalis and of relatively immobile elements including aluminium and rare earth element
Rare earth element
As defined by IUPAC, rare earth elements or rare earth metals are a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides plus scandium and yttrium...
s are subsequently incorporated into precipitating cyrilovite, lipscombite and crandallite-group minerals.
The chemical analysis shows substitution not only of Al for Fe, but also of K and Mn for Na, measured and observed specific gravities
Specific gravity
Specific gravity is the ratio of the density of a substance to the density of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for...
are considered to be in good agreement. Ferric
Ferric
Ferric refers to iron-containing materials or compounds. In chemistry the term is reserved for iron with an oxidation number of +3, also denoted iron or Fe3+. On the other hand, ferrous refers to iron with oxidation number of +2, denoted iron or Fe2+...
iron occurs virtually alone in H20 rich minerals such as phosphosiderite, and coupled with Na, K, or Ca in cyrilovite. It is soluble in hot dilute HCl
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
, in hot dilute H2SO4
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
, and, with difficulty, in hot dilute HNO3
Nitric acid
Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...
. In the closed tube, it gives off water and fuses.
Geologic occurrence
The mineral wardite is capable of crystallizing in a similar form to that of cyrilovite because of their closely related chemical compositions. Between wardite’s composition, NaAl3(PO4)2(OH)4•2(H2O), and cyrilovite’s composition, NaFe3(PO4)2(OH)4•2(H2O), they’re able to form end members of a series of solid solutions. Either of the two minerals can occur in various proportions in a series of solid solutions in the wardite mineral group. Cyrilovite is a rare accessory mineral in some oxidizing phosphate-bearing granite pegmatitles and iron deposits. The sequence of phosphate transformations ended with the formation of cyrilovite within the F-apatite factures and the replacement of F-apatite by lipscombite and crandillite-group minerals. Weathering related cyrilovite, lipscombite, and crandillite-group minerals were formed by percolating meteoric waters under increasing oxygen fugacity
Fugacity
In chemical thermodynamics, the fugacity of a real gas is an effective pressure which replaces the true mechanical pressure in accurate chemical equilibrium calculations. It is equal to the pressure of an ideal gas which has the same chemical potential as the real gas. For example, nitrogen gas ...
.
Structure
The crystal structures of natural wardite and of the isomorphous cyrilovite have the space group
Space group
In mathematics and geometry, a space group is a symmetry group, usually for three dimensions, that divides space into discrete repeatable domains.In three dimensions, there are 219 unique types, or counted as 230 if chiral copies are considered distinct...
P41212, Z=4). Hydrogen atoms were not located, but reasonable positions can be estimated. The cell dimentsions of cyrilovite are: c=19.4, a=7.32 Å
Ångström
The angstrom or ångström, is a unit of length equal to 1/10,000,000,000 of a meter . Its symbol is the Swedish letter Å....
.
The individual crystals are usually smaller than 0.1 mm and many of them are intergrown. Crystals are squat and when single tend to lie on the basal pinacoid. The pinacoid {001} and the dipyramid {113} are the dominant forms; all the faces of thse forms tend to be present and equally well developed. The dipyramid {012} is not always present. The direction for the a-axis is at 45° angle to the smallest primitive unit cell.