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).^[2]

Dessauite-(Y)
General
Category	Oxide mineral Crichtonite group
Formula	(Sr,Pb)(Y,U)(Ti,Fe3+ ) 20O 38
IMA symbol	Dss-Y[1]
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/cm3 (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.^[3] The difference between dessauite and other minerals in the crichtonite 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 0.2 mm. In reflected plane-polarized light the color is ash-grey with pale bluish tones.^[2] 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.^[4] 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.^[2]

See also

• List of minerals