Dessauite-(Y)

Dessauite-(Y) is a mineral member of the crichtonite group with the formula (Sr,Pb)(Y,U)(Ti,Fe³⁺
)
₂₀O
₃₈. It is associated with derbylite, hematite, rutile, karelianite, siderite, and calcite. Founded in the Buca della Vena Mine, Tuscany, Italy, the mineral was called dessauite in honor of professor Gabor Dessau (1907–1983).[1]

Dessauite-(Y)
General
Category	Oxide mineral Crichtonite group
Formula (repeating unit)	(Sr,Pb)(Y,U)(Ti,Fe^3+ ) 20O 38
Strunz classification	4.CC.40
Crystal system	Trigonal
Crystal class	Rhombohedral (3) H-M symbol: (3)
Space group	R3
Unit cell	a = 9.197 Å, α = 68.75°
Identification
Formula mass	1,856.57 g/mol
Color	Black; ash-grey with pale bluish tones.
Crystal habit	Tabular
Cleavage	None
Fracture	Conchoidal
Tenacity	Brittle
Mohs scale hardness	​6 ^1⁄2 - 7
Luster	Metallic luster
Streak	Black
Diaphaneity	Opaque
Density	4.68 g/cm^3 (calculated)
Birefringence	Low
Pleochroism	Very weak

Structure

Dessauite occurs as small, flattened rhombohedral crystals, tabular {001} with hexagonal outline. Members of the Crichtonite group may be confused with ilmenite or hematite.[2] The difference between dessauite and other minerals in the crichonite group is the occurrence of three additional octahedral sites and of a site in square pyramidal coordination, all with low occupancies. The mineral is black and opaque, presents a metallic luster, and it is brittle. Dessauite presents dimensions of diameter up to 1mm and thickness up to 0.2mm. In reflected plane-polarized light the color is ash-grey with pale bluish tones.[1] The calculated density is 4.68 g/cm³. The habit is tabular, forming thin dimensions in one direction and hardness of 6.5 and 7.[3] Dessauite differs from other elements of the crichtonite group because of the quantity of cations and X-ray diffraction pattern.

Occurrence

Dessauite was found in the Buca della Vena Mine, Apuan Alps, northern Tuscany, Italy, with many other minerals, coming from hydrothermal fluids circulating through a small hematite-barite ore deposit within dolomite, during an alpine metamorphic event. It occurs in calcite veins hosted within dolomite and is associated with calcite, rutile, hematite, siderite, and derbylite.[1]

See also

• List of minerals

References

1. Orlandi, Paolo (1997). "Dessauite, (Sr,Pb)(Y,U)(Ti,Fe3+)20O38, a new mineral of the crichtonite group from Buca della Vena mine, Tuscany, Italy" (PDF). Journal of the Mineralogical Society of America.
2. "Crichtonite Group".
3. "Dessauite Mineral Data". www.webmineral.com. Retrieved 2015-12-02.