Minyulite is a rare

phosphate mineral Phosphate minerals are minerals that contain the tetrahedrally coordinated phosphate () anion, sometimes with arsenate () and vanadate () substitutions, along with chloride (Cl−), fluoride (F−), and hydroxide (OH−) anions, that also fit in ...

with a

chemical formula A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as pare ...

of (redefinition, IMA21-E). It occurs as groups of radiating fine fibrous crystals within rock cracks of phosphatic

ironstone Ironstone is a sedimentary rock, either deposited directly as a ferruginous sediment or created by chemical replacement, that contains a substantial proportion of an iron ore compound from which iron (Fe) can be smelted commercially. Not to be c ...

. Minyulite belongs to the orthorhombic

crystal system In crystallography, a crystal system is a set of point groups (a group of geometric symmetries with at least one fixed point). A lattice system is a set of Bravais lattices (an infinite array of discrete points). Space groups (symmetry groups ...

. This indicates that it has three axes of unequal length yet all are perpendicular to each other. Its cell constants are a=9.35, b=9.74 c=5.52. As for its optical properties, Minyulite is an

anisotropic Anisotropy () is the structural property of non-uniformity in different directions, as opposed to isotropy. An anisotropic object or pattern has properties that differ according to direction of measurement. For example, many materials exhibit ver ...

mineral which means the velocity of light differs when traveling through it depending on the cut of its cross-section which gives it more than one refractive index.Klein, C., and Dutrow, B.(2007) The 23rd Edition of the Manual of Mineral Science, 290 p. John Wiley and Sons, Inc. Hoboken, New Jersey, U.S.A. The mineral is optically biaxial. Its

birefringence Birefringence, also called double refraction, is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are described as birefrin ...

value is 0.007. It has three

refractive indices In optics, the refractive index (or refraction index) of an optical medium is the ratio of the apparent speed of light in the air or vacuum to the speed in the medium. The refractive index determines how much the path of light is bent, or refrac ...

which are nα=1.531 nβ=1.534 nγ=1.538. Refractive indices are a ratio of the speed of light in a median with respect to the speed of light passing through the mineral.

Occurrence

It was first described in 1933 for an occurrence in Western Australia and named after the type locality, Minyulo Well in

Western Australia Western Australia (WA) is the westernmost state of Australia. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to the south, the Northern Territory to the north-east, and South Australia to the south-east. Western Aust ...

. Minyulite is considered as a secondary phosphate since it is formed by the alteration of a primary phosphate. It occurs in association with dufrenite,

apatite Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of Hydroxide, OH−, Fluoride, F− and Chloride, Cl− ion, respectively, in the crystal. The formula of the admixture of ...

, fluellite,

wavellite Wavellite is an aluminium basic phosphate mineral with formula aluminium, Al3(phosphorus, Poxygen, O4)2(Ohydrogen, H, fluorine, F)3·5water, H2O. Distinct crystals are rare, and it normally occurs as translucent green radial or spherical clusters ...

variscite Variscite is a hydrated aluminium phosphate mineral (). It is a relatively rare phosphate mineral. It is sometimes confused with turquoise; however, variscite is usually greener in color. The green color results from the presence of small amounts ...

and leucophosphite. The mineral can be found in the underlying phosphatized rock zone of ornithogenic soil. Minyulite is not found in abundance, it can be found in the seashore of the maritime Arctic. Tatur, A., and Keck, A. (1990) Phosphates in ornithogenic soils of the Maritime Antarctic.Proc. NIPR Symp. Polar Biol: 3, 133-150.

References

{{Commonscat Phosphate minerals Orthorhombic minerals Minerals in space group 32 Potassium minerals Aluminium minerals