Dessauite-(Y)

Dessauite-(Y)
General
Category Oxide mineral
Crichtonite group
Formula
(repeating unit)		 (Sr,Pb)(Y,U)(Ti,Fe3+)20O38
Crystal system Trigonal
Unit cell a = 9.197 Å, α = 68.75°
Identification
Formula mass 1,856.57 gm
Color Black; ash-grey with pale bluish tones.
Crystal habit Tabular
Cleavage None
Fracture Conchoidal
Tenacity Brittle
Mohs scale hardness 6½ - 7
Luster Metallic luster
Streak Black
Diaphaneity Opaque
Density 4.68 g/cm3 (calculated)
Birefringence Low
Pleochroism Very 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

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 patter.

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

References

  1. 1 2 3 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.


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