Childrenite

Childrenite
Childrenite from Galileia, Minas Gerais, Brazil 2 cm across
General
Category	Phosphate minerals
Chemical formula	(Fe2+,Mn2+)AlPO4(OH)2·H2O
Strunz classification	08.DD.20
Crystal symmetry	Orthorhombic dipyramidal H–M Symbol mmm (2/m 2/m 2/m)
Unit cell	a = 10.41 Å, b = 13.42 Å, c = 6.92 Å
Identification
Color	Yellowish brown, brown, clove-brown; colorless in transmitted light.
Crystal system	Orthorhombic
Cleavage	Poor/indistinct on {100}
Fracture	Irregular/uneven, sub-conchoidal
Mohs scale hardness	5
Luster	Vitreous, resinous
Streak	White
Diaphaneity	Transparent, translucent
Specific gravity	3.11 - 3.19
Optical properties	Biaxial (-)
Refractive index	nα = 1.644 - 1.649 nβ = 1.662 - 16.830 nγ = 1.671 - 1.691
Birefringence	δ = 0.027 - 0.042
Pleochroism	Visible
2V angle	Measured: 40° to 45°, calculated: 50°
Dispersion	r > v strong
Solubility	Soluble in acids.
References	[1][2]

Childrenite is a rare hydrated phosphate mineral with elements iron, manganese, aluminium, phosphorus, oxygen and hydrogen. Its chemical formula is (Fe,Mn)AlPO₄(OH)₂ • H₂O and it has a molecular weight of 229.83 g/mol. Its specific gravity is 3.2 and it has a Mohs hardness of 4.5 to 5. It is usually translucent and non-fluorescent, with imperfect cleavage. It has a vitreous lustre with a white streak, and is brown or yellow in color. It has a conchoidal, uneven fracture, and an orthorhombic crystal system.

History and formation

Childrenite was discovered in 1823 by John George Children (1777 - 1852), who was a prominent English chemist and mineralogist. This secondary mineral was first found in the George and Charlotte Mine near Tavistock in Devon. Its formation is probably from the alteration of granitic phosphates like lithiophilite and triphylite. Childrenite is also found in some ore veins.

Relationship to other species

Childrenite forms a solid solution series with eosphorite. The chemical composition of eosphorite only differs by being rich in manganese and not in iron. The structures are the same, and differences in properties can be traced to the iron/manganese percentage. Of the two, childrenite is denser. Furthermore, eosphorite is normally pink in color, which can be attributed to manganese.

References

1. ^ MinDat
2. ^ WebMineral

• Mineral Galleries
• Athena Minerals
• University of Delaware