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Brenkite is a rare calcium fluor-carbonate mineral
== Abstract: The mineral brenkite (Ca2F2(CO3)), pronounced bren-kite, is a calcium fluor-carbonate group mineral which has the characteristics of the orthorhombic crystal system. It was first discovered in 1978 by Dr. G. Hentschel, Wiesbaden in Schellkopf, Eifel, Germany (Leufer et. al., 1980). It occurs in narrow openings produced by cleavage in porphryritic selbergite. It is closely related to phillipsite, zeophyllite, gismondine, and calcite. (Republished by the Mineralogical Society of America) ==
== Introduction:
Brenkite is a member of the calcium fluor-carbonates which are classified by bonding between Ca-F and C-O forming tetrahedral polyhedra that share edges and corners that creates a 4-fold ring and an internal structure, rather than layers (Leufer et. al., 1980). Brenkite is a fairly new mineral, being discovered in 1978 (Leufer et. al., 1980) and is quite rare. It is not used commercially for any purpose and has no significant effect economically. ==
== Composition: The chemical formula of brenkite is Ca2F2(CO3) and has a molecular weight of 178.16 gm (Leufer et. al., 1980). The calculated weight percent oxides is illustrated below:
Table 1-a. Chemical composition of brenkite in wt % oxides (Republished by the Mineralogical Society of America)
| Chemistry | (1) | (2) | |
|---|---|---|---|
| CO2 | 24.6 | 24.70 | |
| CaO | 62.3 | 62.95 | |
| F | 21.3 | 21.33 | |
| -O = F2 | 9.0 | 8.98 | |
| Total | 99.2 | 100.00 |
==
== Structure:
Brenkite is in the Orthorhombic dipyramidal system with 3 2-fold axes, down the [100], [010], and [001], and each having a mirror plane perpendicular to them. It has the Hermann–Mauguin notation symbol of 2/m 2/m 2/m. To make its structure, a calcium is coordinated by four flourine and three oxygen atoms to form a tetrahedral structure. Once these are combined they form a 4-fold ring polyhedra. The polyhedra are connected by edges and cornes with a carbonate group in between forming a framework. Podlesnoite has a similar structure, but instead of forming a structure, it forms layers (Zubkova et. al., 2007). The Ca-F and Ca-O have an average distance of 2.388 and 2.426 Å, whereas the CO3 groups are flat with the C-O distances at 1.279 (2x) and 1.297 Å (Leufer et. al., 1980). Another mineral that has similar inter-atomic distances is zeophyllite, which has irregurarly coordinated F and Ca polyhedra (Mikenda et. al., 1997). Looking down the {100} and the {010} axes, brenkite is flattened, and down the {001} axis the internal framework of the structure becomes more clear. Brenkite crystallizes in space group Pbcn where a = 7.650(2) , b = 7.550(2) , and c = 6.548(2) Å, Z=4, G (calc) = 3.126, (meas) = 3.10 ± 0.04 (Fleischer et. al., 1979). ==
== Physical Properties:
Brenkite is a colorless mineral that grows in radially formed crystal aggregates which are flat along the {010} and along the [001] are elongated. All these factors combined, and brenkite will only grow to 6mm, in radial or spherical crystals. It leaves a white streak on a plate, has a hardness of 5, a specific gravity of 3, and no distinct cleavage. Brenkite effervesces in dilute HCl (Fleischer et. al., 1979). ==
== Geologic Occurrence:
Brenkite normally occurs in narrow openings produced by cleavage in porphryritic selbergite, and formerly nonsean-phonolite (Republished by the Mineralogical Society of America). It was named for its location it was discovered in, Brenk. Outside of Brenk, it only is found in Point of Rocks Quarry, Springer, New Mexico. ==
== Literature Survey:
The most highly cited paper on Brenkite was on the Web of Science which was Leufer and Tillmann’s “The Crystal-Structure of Brenkite Ca2F2(CO3)” (1980) with nine citations. Leufer and Tillmann actually wrote about brenkite previously in 1978, not long after it was first discovered by Dr. G. Hentschel, Wiesbaden, though it is not displayed in the Web of Science, but a more thorough report was conducted two years later by them which is the paper mentioned above (Leufer et. al., 1980). Also, the text is only available in German, with no other translations available which makes it very difficult to study. ==
== Prospects for further research:
A new study of brenkite has not yet been conducted since (and the last study of brenkite used the single-crystal method), so there is a huge gap in any literature has been dedicated to the study of brenkite and the current information available is vague compared to the accuracy that can be produced now. If a sample was able to be acquired by the University of Houston, brenkite could be reevaluated to find out many new things about it and possible new applications. Possible studies that could be conducted would include X-ray powder diffraction and X-ray spectroscopy among others. ==
References
edit- ^ Leufer U., Tillmanns E., (1980) The Crystal-Structure of Brenkite, Ca2F2CO3. Tschermaks Mineralogische Und Petrographische Mitteilungen, Vol 27, Issue 4, 261-266.
- ^ Fleischer M., Chao G.Y., and Pabst A., (1979) New Mineral Names. American Mineralogist, 64, 241-242.
- ^ Mikenda W., Pertlik F., Povondra P., and Ulrych J., (1997) One zeophyllite from Radejcin, Ceske stredohori Mts.: X-ray and IR-investigations. Mineralogy and Petrology, Vol 61, 199-209.
- ^ Zubkova N.V., Pushcharovsky D.Y., Pekov I.V., Rabadanov M.K., (2007) The Crystal Structure of Podlesnoite, BaCa2(CO3)(2)F-2. Zeitschrift Fur Kristallographie, Vol 222, Issue 9, 474-476.
- ^ Brenkite Ca2F2(CO3). Handbook of Mineralogy. Mineral Data Publishing
- ^ Witzke T., and Abraxas V., Brenkite Ca2(CO3)F2. Web
External links
editEntry on mindat.org[1] Entry on webmineral.com[2] Handbook of Mineralogy[3]