Ransomite
General
CategorySulfate
Formula
(repeating unit)		CuFe2(SO4)4*6H2O
Crystal systemMonoclinic
Crystal class2/m - Prismatic
Space groupP21/b
Unit cella = 4.811 Å, b = 16.217 Å
c = 10.403 Å;
β= 93.01°; Z = 2
Identification
Formula mass667.59
ColorBright sky blue; pale blue in transmitted light
Crystal habitneedle-like crystals
CleavagePerfect along {010}
TenacityRadiating tufts and crusts
Mohs scale hardness2.5
LusterVitreous, pearly cleavage
DiaphaneityTransparent
Density2.632 g/cm3
Optical propertiesBiaxial positive
Refractive indexnα= 1.631 nβ= 1.643 nγ= 1.695
Birefringenceδ = 0.064
Dispersionv > r strong
References[1][2][3]

Ransomite is a sulfate mineral first discovered at the United Verde mine in Jerome Arizona. This mineral was formed as a result of a mine fire. The United Verde mine is one of few places in the world where Ransomite can be found. This mineral can be described as a soluble sulfate that forms needle-like crystals and has a pale blue color in transmitted light.[1] This mineral was named by Carl B. Lausen as a tribute to Frederick Leslie Ransome. Ransome was an American mining geologist who worked at the California Institute of Technology, the University of Arizona and the United states Geological Survey.[2]

Occurrence

Ransomite is found in association with pyrite, voltaite, and romerite. These minerals can be found in Campbell shaft, Arizona.[3] Ransomite tends to form in the cavities of crushed up rock in these different mines. In these cavities, Ransomite forms small radiating crystals and pale-blue crusts.[1]

Physical properties

Ransomite is a bright sky blue or a pale blue in transmitted light, transparent mineral with a vitreous, pearly luster. It exhibits a hardness of 2.5 on the Mohs hardness scale.[2] Ransomite occurs as needle-like crystals and has radiating tufts and crusts. Ransomite has perfect cleavage along the {010} plane. The specific gravity is 2.632 g/cm3.[2]

Optical properties

Ransomite is biaxial positive, this means it can refract light on two axes. The refractive indices are: α ~ 1.631, β ~ 1.643, and γ ~ 1.695 (Na). Dispersion is strong, v > r. Ransomite has a max birefringence of 0.064 and has a moderate surface releif. [2]

Chemical properties

Ransomite is a sulfate that has a similair formula to the mineral Cuprocopiapite. Cuprocopiapite has a specific gravity of (2.23 g cm−3), which is close to the value of Ransomite. [2]

Chemical composition

Oxidewt%
SO346.30
Al3O31.52
Fe2O322.57
CuO11.29
H2O18.82
Total100.50

[3]

X-ray crystallography

Ransomite is in the monoclinic crystal system. The space group associated with Ransomite is P21/b with unit cell dimensions: a = 4.811Å, b = 16.217Å, c = 10.403Å; β= 93.01°; Z=2. Ransomite has a point group of 2/m and is prismatic. It also has skinny prisms extended parallel to the c axis. [2]

References

  1. 1 2 3 Wood, M.M., 1970, The Crystal Structure of Ransomite, The American Mineralogist, v. 55, p.729-734
  2. 1 2 3 4 5 6 7 Hudson Institute of Mineralogy, 2023, Ransomite: https://www.mindat.org/min-3364.html (accessed November 2023)
  3. 1 2 3 Mineral Data publishing, 2001-2005, Ransomite: https://www.handbookofmineralogy.org/pdfs/ransomite.pdf (accessed November 2023)
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