Sampleite

Sampleite
General
Category	Phosphate minerals
Formula (repeating unit)	NaCaCu5(PO4)4Cl•5(H2O)
Strunz classification	08.DG.05
Crystal symmetry	Orthorhombic (2/m 2/m 2/m) dipyramidal
Unit cell	a = 9.7 Å, b = 38.4 Å, c = 9.65 Å; β = 90.07°; Z = 8
Identification
Formula mass	875.95 g
Color	Light blue to blue-green
Crystal habit	Aggregates, lath, rosette
Crystal system	Orthorhombic
Cleavage	Perfect on {010}; good on {100} and {001}
Mohs scale hardness	4
Luster	Pearly
Streak	Light Blue
Diaphaneity	Transparent
Specific gravity	3.2
Optical properties	Biaxial (-)
Refractive index	nα = 1.629 nβ = 1.677 nγ = 1.679
Birefringence	δ = 0.050
Pleochroism	X = deep blue, blue-green; Y = light blue, turquoise blue; Z = turquoise-blue, colorless
2V angle	Measured: 5° to 23°
References	[1][2][3]

Sampleite has a general formula of NaCaCu₅(PO₄)₄Cl•5(H₂O).^[3] It was first described in 1942 for an occurrence in Chuquicamata, Chile and was named after Mat Sample, a mine superintendent for the Chile Exploration Company.^[2]

Sampleite is orthorhombic, which means crystallographically, it contains 3 unequal axes with angles that are 90°. It belongs to the space group 2/m.^[4] In a thin section it has a high surface relief and will have sharp boundaries with the surrounding medium. Sampleite is anisotropic and has visible pleochroism and birefringence.

It is characteristically found in earthy crusts in a highly sericitized rock and is present in highly oxidized conditions near the surface. When it occurs as micaceous rosettes and aggregates it can be associated with dendrites of manganese and iron oxides. Sampleite appears to be the most recent mineral deposited with the exception of gypsum.^{[5] [6]}

References