Dessauite-(Y)

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Dessauite-(Y)
General
CategoryOxide mineral
Crichtonite group
Formula
(repeating unit)
(Sr,Pb)(Y,U)(Ti,Fe3+)20O38
Strunz classification4.CC.40
Crystal systemTrigonal
Crystal classRhombohedral (3)
H-M symbol: (3)
Space groupR3
Unit cella = 9.197 Å, α = 68.75°
Identification
Formula mass1,856.57 g/mol
ColorBlack; ash-grey with pale bluish tones.
Crystal habitTabular
CleavageNone
FractureConchoidal
TenacityBrittle
Mohs scale hardness6 12 - 7
LusterMetallic luster
StreakBlack
DiaphaneityOpaque
Density4.68 g/cm3 (calculated)
BirefringenceLow
PleochroismVery weak

Dessauite-(Y) is a mineral member of the crichtonite group with the formula (Sr,Pb)(Y,U)(Ti,Fe3+)20O38. 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]

Structure[edit]

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[edit]

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[edit]

References[edit]

  1. ^ a b c 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.