Ransomite

General
Category| Sulfate
Formula
(repeating unit)| CuFe2(SO4)4*6H2O
Crystal system| Monoclinic
Crystal class| 2/m - Prismatic
Space group| P21/b
Unit cell| a = 4.811 Å, b = 16.217 Å
c = 10.403 Å;
β= 93.01°; Z = 2
Identification
Formula mass| 667.59
Color| Bright sky blue; pale blue in transmitted light
Crystal habit| needle-like crystals
Cleavage| Perfect along {010}
Tenacity| Radiating tufts and crusts
Mohs scale hardness| 2.5
Luster| Vitreous, pearly cleavage
Diaphaneity| Transparent
Density| 2.632 g/cm3
Optical properties| Biaxial positive
Refractive index| nα= 1.631 nβ= 1.643 nγ= 1.695
Birefringence| δ = 0.064
Dispersion| v > 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[edit]

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[edit]

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[edit]

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[edit]

Ransomite is a sulfate that has a similar 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[edit]

Oxide | wt%

|

SO3 | 46.30
Al3O3 | 1.52
Fe2O3 | 22.57
CuO | 11.29
H2O | 18.82
Total | 100.50

[3]

## X-ray crystallography[edit]

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[edit]

1. ^ a b c Wood, M.M., 1970, The Crystal Structure of Ransomite, The American Mineralogist, v. 55, p.729-734
2. ^ a b c d e f g Hudson Institute of Mineralogy, 2023, Ransomite: https://www.mindat.org/min-3364.html (accessed November 2023)
3. ^ a b c Mineral Data publishing, 2001-2005, Ransomite: https://www.handbookofmineralogy.org/pdfs/ransomite.pdf (accessed November 2023)