Gottlobite

Gottlobite, CaMg(VO
4
,AsO
4
)(OH
), is a mineral found as isolated crystals or isometric grains of orange or orange-brown color. The size of the crystals are a half millimeter in diameter and are part of the orthorhombic crystal system. Gottlobite forms a solid solution with adelite, which is an end member composition of CaMg(VO4)(OH), as well as being classified in the adelite group. Gottlobite is also part of the vanadates and arsenates group. With these characteristics, it is similar to the minerals tangeite and austinite by X-ray diffraction methods. [3]

Gottlobite
General
CategoryHydroxide mineral, Vanadate mineral, Arsenate mineral
Formula
(repeating unit)
CaMg(VO
4
,AsO
4
)(OH)
Strunz classification08.BH.35
Dana classification41.05.01.10
Crystal systemOrthorhombic
Space groupP222
Unit cella = 7.501(4) Å; b = 9.010(7) Å; c = 5.941(4) Å; Z = 4, V = 401.5Å3
Identification
Formula mass205.20 gm
ColorOrange to orange-brown
Crystal habitIsometric to tabular crystals
TwinningNot observed
CleavageNot observed
FractureConchoidal to irregular
TenacityBrittle
Mohs scale hardness4.5
LusterVitreous to adamantine
StreakLight brownish
DiaphaneityTransparent
Specific gravity3.46 g/cm3 (calculated)
Optical propertiesBiaxial negative
Refractive indexnα = 1.797 nβ = 1.805-1.815 nγ = 1.828
PleochroismMedium strong with X = orange-brown, Y = pale yellowish brown, and Z = orange-brown
GroupVandates and Arsenates
References[1][2][3]

Occurrence

Gottlobite is a relatively rare mineral where only a small quantity of the mineral has been found. It was first observed at the site of a long-abandoned mine on the northern slope of Gottlob hill in Friedrichroda, Thuringia, Germany by Jὒrgen Graf in August of 1996. As such, gottlobite got its name from its locality. Additionally, the German translation of "Lob" means "praise" and the German translation of "Gott" means "God," as deciphered by Google Translate. In the mine at this location, Gottlobite is found in hydrothermal veins of barite that are cutting through conglomerate. The crystals of gottlobite can be found embedded in these barite veins or as stand-alone crystals on surrounding minerals. The associated minerals in the area are hausmannite, barite, vanadian adelite, and muscovite. [3]

Composition

Analytical methods used on gottlobite to determine its chemical composition include energy-dispersive X-ray spectrometry (EDX) and wavelength-dispersive X-ray spectrometry (WDX). EDX revealed the presence and quantities of elements present in the mineral, including Ca, V, As, O and small amounts of Sr. This was then measured in terms of oxides, where the weight percents were 24.98 for CaO, 0.92 for SrO, 17.54 for MgO, 1.50 for MnO, 1.44 for CuO, 27.47 for V2O5, 20.32 for As2O5, and 5.4 for H2O. Mg is in gottlobite's chemical formula, but was not found in the EDX testing because of very similar pattern of arsenic lines that were overlapping with magnesium. The full empirical formula of gottlobite is (Ca
0.93
,Sr
0.03
)(Mg
0.91
,Mn
0.04
,Cu
0.04
)(V
0.63
,As
0.37
)O
4
O
1.08
H
1.26
. As seen in the formula, it was also determined that the arsenic and vanadium atoms are in 4-fold (tetrahedral) coordination with oxygen, and the magnesium atoms are in six-fold (octahedral) coordination. [3]

See also

References

  1. Gottlobite. Webmineral. Retrieved on 2017-11-24.
  2. Journal. Retrieved on 2017-11-17.
  3. Witzke, T.; Steins, M.; Doering, T.; Kolitsch, U. (2000). "Gottlobite, CaMg(VO4, AsO4)(OH), a new mineral from Friedrichroda, Thuringia, Germany". Neues Jahrbuch für Mineralogie - Monatshefte. Monatshefte 2000: 444–454.
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