Karlite

Karlite
General
Category Borate mineral
Formula
(repeating unit)		 Mg7(BO3)3(OH)4Cl
Strunz classification 6.AB.25
Crystal system Orthorhombic
Crystal class Disphenoidal (222)
H-M symbol: (222)[1]
Space group P212121[1]
Identification
Formula mass 412.74 g/mol
Crystal habit Acicular, fibrous, rosette like and fibrous aggregates
Cleavage Perfect on {001}
Mohs scale hardness ​5 1⁄2
Luster Silky
Streak White
Diaphaneity Semitransparent
Specific gravity 2.80-2.85
Optical properties Biaxial (-)
Refractive index nα = 1.589 nβ = 1.632 nγ = 1.634
Birefringence δ = 0.045
References [1][2]

Karlite (kar'-lite) is a silky white to light green orthorhombic borate mineral, not to be confused with tremolite-actinolite. It has a general formula of Mg7(BO3)3(OH)4Cl.[3] Karlite is named in honor of Franz Karl (1918–1972), professor of mineralogy and petrography at Christian Albrechts University in Kiel, Germany, for his studies of the geology of the eastern Alps.

Karlite possesses moderate optical relief, the degree to which the mineral grains stand out from the mounting medium. This mineral is orthorhombic and sphenoidal, exhibiting symmetry on 222. Karlite is also enantiomorphic and dihedral. It is a member of the P212121 space group. This mineral forms optically negative biaxial birefringent crystals, meaning that the 2V angle between the optic axes is bisected by the refractive index direction. Because this mineral possesses birefringence, we know it is anisotropic and will display double refraction; it breaks light into two different rays traveling at different speeds in the mineral.

Karlite is a relatively newly discovered borate mineral occurring in clinohumite-chlorite marble in calcsilicate-carbonate lenses embedded in amphibolite. The amphibole at the original locale is situated between tectonic units “Zentralgneis” and “Schieferhulle”. Scholars assume that the high boron concentration needed for the formation of karlite is due to a contact metasomatism created by Hercynian tonalitic magmas, which make up the “Zentralgneis", although the boron content of karlite is not of commercial importance.[4] This mineral was originally discovered in the Furtschaglkar near the Furtschaglhaus in Austria, but has also been found in Russia and France, and was probably formed during the alpine metamorphism of the Alps.[1][5]

References

  1. 1 2 3 4 Franz, Gerhard; Ackermand, Dietrich; Koch, Eddie (1981). "Karlite, Mg7(BO3)3(OH,Cl)4 a new borate mineral and associated ludwigite from the Eastern Alps." American Mineralogist, 66, 872–877.
  2. ↑ Roberts, William Lincoln, Thomas J. Campbell, and George Robert Rapp, Jr., "Karlite." Encyclopedia of Minerals. 2nd ed. N.p.: Springer, 1990. Print
  3. ↑ http://glossary.agiweb.org/
  4. ↑ Polyak, Desiree E. "Boron." U.S. Geological Survey Minerals Yearbook. N.p.: n.p., 2007. 13.8-13.10. Print.
  5. ↑ Bonazzi, P., et al. "Karlite: Crystal Structure and Composition." Neues Jahrbuch fur Mineralogie, Monatshefte (1986): 253-262. Print.
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