Roselite

Roselite is a rare arsenate mineral with chemical formula: Ca₂(Co,Mg)[AsO₄]₂·H₂O. It was first described in 1825 for an occurrence in the Rappold mines of Schneeberg, Saxony, Germany and named by Armand Lévy after German mineralogist Gustav Rose.^[2] It occurs in cobalt-bearing hydrothermal environments and was associated with veins of quartz and chalcedony in the type locality.^[2][4] It has also been reported from Italy, Morocco, Chile, British Columbia and several locations in Germany.^[2]

Roselite
General
Category	Arsenate minerals
Formula	Ca2(Co2+, Mg)[AsO4]2·H2O+
IMA symbol	Rsl[1]
Strunz classification	8.CG.10
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P21/c
Unit cell	a = 5.801 Å, b = 12.898 Å c = 5.617 Å; β = 107.42°; Z = 2
Identification
Color	Dark rose red, pink
Crystal habit	Elongated crystals and spherical aggregates and druses
Twinning	Common as composition plane, contact twins and fourlings
Cleavage	{010} Perfect
Mohs scale hardness	3.5
Luster	Vitreous
Streak	Light red
Specific gravity	3.69
Optical properties	Biaxial (−)
Refractive index	nα = 1.725 nβ = 1.728 nγ = 1.735
Pleochroism	(Dark rose) X: Dark rose, Y: Pale rose, Z: Paler rose (Light rose) X: Pale rose, Y: Paler rose, Z: Palest rose
2V angle	Calculated: 68°
References	[2][3][4]

The pleochroism of roselite depends on chemical composition with darker-rose-colored varieties higher in cobalt content and lighter-rose-colored varieties higher in calcium and magnesium content (Palache et al., 1960). This gives rise to two different pleochroism schemes, one for dark rose and one for light rose. Dark rose varieties have X: dark rose, Y: pale rose, Z: paler rose. Light rose varieties have X: pale rose, Y: paler rose, Z: palest rose.