Benstonite

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Benstonite
Benstonite-Calcite-37920.jpg
Benstonite with calcite
General
Category Carbonate minerals
Formula
(repeating unit)
Ba6Ca6Mg(CO3)13[1]
Strunz classification 05.AB.55
Dana classification 14.2.3.1
Crystal symmetry H-M group: 3 Rhombohedral
Space group: R3
Unit cell a = 18.280Å, c = 8.652Å
Z = 3
Identification
Color Snow-white, ivory, very pale yellow, pale yellowish brown[2]
Crystal system Trigonal
Cleavage Good on {3142}[2]
Mohs scale hardness 3–4
Luster Vitreous
Streak White
Diaphaneity Translucent
Optical properties Uniaxial (-)
Refractive index nω = 1.690 nε = 1.527
Birefringence δ = 0.163
Ultraviolet fluorescence Red or yellow under UV and X-rays[2]
References [3]

Benstonite is a mineral with formula Ba6Ca6Mg(CO3)13.[1] Discovered in 1954, the mineral was described in 1961 and named after Orlando J. Benston (1901–1966).

Description and occurrence[edit]

Benstonite is translucent and white, pale yellow, or pale yellow-brown in color.[2] The mineral occurs as cleavable masses; cleavage fragments are nearly perfectly rhombohedral in shape. Cleavage faces are up to 1 cm (0.39 in) across and slightly curved. On large specimens, the faces exhibit a mosaic structure similar to that in some specimens of dolomite and siderite.[4] Benstonite fluoresces red or yellow under x-rays and longwave and shortwave ultraviolet. The mineral also exhibits strong red phosphorescence.[2]

Benstonite is known to occur in Canada, China, India, Italy, Namibia, Russia, Sweden, and the United States.[3] It occurs in association with alstonite, barite, barytocalcite, calcite, daqingshanite, fluorite, huntite, monazite, phlogopite, pyrite, sphalerite, strontianite, and quartz.[2]

Synthesis[edit]

The mineral was first synthesized in 1973 during a study of the Ba-Mg-Ca-CO3 system in aqueous solution. At room temperature, a solution containing proportional quantities of magnesium chloride, barium chloride, and calcium chloride was prepared, to which sodium carbonate was added. The solution immediately precipitated, and after sitting for two weeks, the precipitate was identified as nearly pure benstonite.[5]

History[edit]

Orlando J. Benston[3] of Malvern, Arkansas, visited a barite mine near the Magnet Cove igneous complex on New Year's Eve, 1954. He collected samples of a mineral that he guessed might be alstonite or barytocalcite on the basis of qualitative tests.[6] Friedrich Lippmann identified it as a new mineral and described it in the journal Naturwissenschaften in 1961.[7] He named it Benstonite in honor of Benston.[4]

Type specimens are held at Victor Goldschmidt University in Germany and the National Museum of Natural History in the United States.[2]

References[edit]

  1. ^ a b "The New IMA List of Minerals – A Work in Progress – Update: November 2012" (PDF). Commission on New Minerals, Nomenclature and Classification. International Mineralogical Association. p. 17. Retrieved December 2, 2012. 
  2. ^ a b c d e f g Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W. et al. (eds.). "Benstonite". Handbook of Mineralogy. Chantilly, VA: Mineralogical Society of America. 
  3. ^ a b c "Benstonite". Mindat. Retrieved December 2, 2012. 
  4. ^ a b Lippmann 1962, p. 586.
  5. ^ Hood & Steidl 1973, p. 341.
  6. ^ Lippmann 1962, pp. 585–586.
  7. ^ Fleischer, Michael (November–December 1961). "New mineral names". The American Mineralogist 46 (11–12): 1517. 
Bibliography

Further reading[edit]

External links[edit]

Media related to benstonite at Wikimedia Commons