Valentinite

Valentinite
A sample of valentinite from Algeria (size: 6.9 x 4.4 x 3.3 cm)
General
Category	Oxide minerals
Formula (repeating unit)	Sb2O3
Strunz classification	4.CB.55
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Pccn
Unit cell	a = 4.91 Å, b = 12.46 Å c = 5.42 Å; Z = 4
Identification
Color	Colorless, snow-white, pale yellow, pink, gray to brownish
Crystal habit	Prismatic crystals, sometimes flattened, fan-shaped or stellate aggregates of crystals; lamellar, columnar, granular, massive.
Cleavage	{110}, perfect; {010}, imperfect
Tenacity	Brittle
Mohs scale hardness	2.5–3
Luster	Adamantine, pearly on cleavages
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	5.76
Optical properties	Biaxial (-)
Refractive index	nα = 2.180 nβ = 2.350 nγ = 2.350
Birefringence	δ = 0.170
2V angle	Very small
References

Valentinite is an antimony oxide mineral with formula Sb₂O₃. Valentinite crystallizes in the orthorhombic system and typically forms as radiating clusters of euhedral crystals or as fibrous masses. It is colorless to white with occasional shades or tints of yellow and red. It has a Mohs hardness of 2.5 to 3 and a specific gravity of 5.76. Valentinite occurs as a weathering product of stibnite and other antimony minerals. It is dimorphous with the isometric antimony oxide senarmontite.

A mineral named in the middle of the 19th century in honour of Basilius Valentinus, a writer on alchemy. He is the supposed author of the first book to give a detailed description of antimony and its compounds. From the contents of the book it is also obvious that Valentinus was familiar with the synthetic preparation of antimony trioxide, which was called 'the antimony flower'.

Valentinite was first described in 1845 for an occurrence in the Les Chalanches Mine, Allemont, Isère, Rhône-Alpes, France. The first description of its occurrence in the region of Pribram in Bohemia comes roughly from the same time. This particular locality at one time produced the very best crystals of this mineral. The largest crystals found there measured up to 3 cm. Grouped in rich druses, they developed in vein cavities with galena.

Valentinite is a weathering product of hydrothermal antimony-bearing veins, where it forms as a secondary mineral through oxidation in the upper parts of the deposits. It occurs associated with stibnite, native antimony, stibiconite, cervantite, kermesite and tetrahedrite.