Raygrantite is a mineral first discovered in Big Horn Mountains, Maricopa County, Arizona, US.[3] More specifically, it is located in the evening star mine, which is a Cu, V, Pb, Ag, Au, and W mine.[1] Raygrantite is a member of the iranite mineral group, which consists of hemihedrite, iranite, and raygrantite.[2] This mineral received its name in honor of Raymond W. Grant, a retired professor who primarily focused on the minerals of Arizona.[1] The typical crystal structure of raygrantite is bladed with parallel striations to the C axis. Its ideal chemical formula is Pb10Zn(SO4)6(SiO4)2(OH)2.[1] The IMA (International Mineralogical Association) approved raygrantite in 2013, and the first publication regarding this mineral was put forth in 2017.[3]

Raygrantite
General
CategoryMineral
Formula
(repeating unit)
Pb10Zn(SO4)6(SiO4)2(OH)2
Crystal systemTriclinic
Crystal class1 – Pinacoidal
Space groupP1
Unit cella = 9.3175(4) Å, b = 11.1973(5) Å
c = 10.08318(5) Å;
Identification
Formula mass2888
ColorNo color
Crystal habitBladed crystals
TwinningFishtail twining axis along [121] – twin axis along [010]
CleavageGood along {120}
FractureUneven
TenacityBrittle
Mohs scale hardness3
LusterVitreous
StreakWhite
DiaphaneityTransparent
Density6.374 g/cm3
Optical propertiesBiaxial positive
Refractive indexnα = 1.915(7) nβ = 1.981(7) nγ = 2.068(9)
Birefringenceδ = 0.153
Dispersionv < r strong
Absorption spectraZ>Y>X
SolubilityInsoluble in water, acetone, and hydrochloric acid
References[1][2][3]

Occurrence

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Raygrantite is associated with cerussite, galena, mattheddleite, lanarkite, leadhillite, anglesite, alamosite, hydrocerussite, diaboleite, and caledonite.[3] Crystals were found in pockets encased in masses of galena.[1] Raygrantite is a secondary mineral and is the result of pyrite-galena-chalcopyrite veins. In this district of the Rocky Mountains, intrusions can date back to the late Cretaceous period.[1]

Physical properties

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Raygrantite is a colorless, transparent mineral that occurs in bladed crystal structures.[2] This bladed structure has striations parallel to the C-axis.[1] Its luster is vitreous, which means it looks similar to glass. Raygrantite on the Mohs hardness scale is a three, which is .5 softer than a penny. It exhibits brittle tenacity and has good cleavage along the {120} plain.[2] This mineral also has characteristic fishtail twinning along the {121} in addition to a twin axis along the {010}. This mineral's recorded density is 6.374 g/cm3.[1]

Optical properties

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Raygrantite is transparent with a vitreous luster. It is biaxial positive, which means it will refract light along two axes.[2] The mineral's 2Vmeas. 76° (2) and 2Vcalc. 85°. The refractive indices are: nα= 1.915(7) nβ= 1.981(7) nγ= 2.068(9).[3] Dispersion is strong, v < r. Raygrantite also exhibits absorption spectra of Z>Y>X.[1]

Chemical structure

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Raygrantite is isotypic with iranite and hemihedrite.[2] When looking at the chemical structure of the iranite mineral group, there are 10 symmetrically independent non-H cation sites. Of these sites, five are filled by lead Pb2þ (Pb1, Pb2, Pb3, Pb4, and Pb5).[1] Then three are filled by S6þ (S1, S2, and S3).[1] Finally, one of the sites is filled by Si4þ, and the last is filled by Zn2þ. Raygrantite is composed of layers of tetrahedron and octahedron joined together by lead ions.[2]

Chemical composition

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Oxide wt%
SiO2 4.30
SO3 16.49
PbO 74.91
ZnO 2.59
H2O [0.62]
Total 98.81

[3]

X-ray crystallography

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To collect this data, a Bruker X8 APEX2 CCD X-ray diffractometer equipped with graphite-monochromatized MoKa radiation was used.[1] Through these analyses, we can understand that Raygrantite is a member of the triclinic crystal system. It was also noted that the space group of this mineral is 1 – Pinacoidal.[2] The next conclusion that can be drawn from the X-ray diffraction data is the unit cell dimensions. These are as such: a = 9.3175(4) Å, b = 11.1973(5) Å
c = 10.08318(5) Å.[1]

See also

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References

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  1. ^ a b c d e f g h i j k l m Yang H., Andrade B. M., Downs T. R., Gibbs B. R., Jenkins A. R. Raygrantite, Pb10Zn(SO4)6(SiO4)2(OH)2, A New Mineral Isostructural With Iranite, From The Big Horn Mountains, Maricopa County, Arizona, USA, The Canadian Mineralogist, 2016, rruff.info/rruff_1.0/uploads/CM54_625.pdf.
  2. ^ a b c d e f g h Slaughter, Dana. “Raygrantite: Mineral Information, Data and Localities.” Mindat.Org, 2017, zh.mindat.org/min-43868.html.
  3. ^ a b c d e f Raygrantite PB10ZN(So4 6(Sio4 2(OH)2 – Handbook of Mineralogy, Mineralogical Society of America, 2017, handbookofmineralogy.org/pdfs/raygrantite.pdf.