Karlite

{{Short description|Borate mineral}} {{Use dmy dates|date=September 2022}} {{Infobox mineral | name = Karlite | category = Borate mineral | boxwidth = | boxbgcolor = | image = Karlite.jpg | imagesize = | caption = | formula = Mg₇(BO₃₎₃(OH)₄Cl | IMAsymbol = Ka<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref> | molweight = 412.74 g/mol | strunz = 6.AB.25 | system = Orthorhombic | class = Disphenoidal (222) <br />H-M symbol: (222)<ref name="Franz"/> | symmetry = ''P''2₁2₁2₁<ref name="Franz"/> | unit cell = | color = | habit = Acicular, fibrous, rosette like and fibrous aggregates | twinning = | cleavage = Perfect on {001} | fracture = | tenacity = | mohs = {{frac|5|1|2}} | luster = Silky | refractive = n_α = 1.589 n_β = 1.632 n_γ = 1.634 | opticalprop = Biaxial (-) | birefringence = δ = 0.045 | pleochroism = | streak = White | gravity = 2.80-2.85 | density = | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Semitransparent | other = | references = <ref name="Franz"/><ref>Roberts, William Lincoln, Thomas J. Campbell, and George Robert Rapp, Jr., "Karlite." Encyclopedia of Minerals. 2nd ed. N.p.: Springer, 1990. Print</ref> }}

'''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.<ref>{{cite web|url=http://glossary.agiweb.org/|title=Karlite|website=agiweb.org}}</ref> 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.<ref>Polyak, Desiree E. "Boron." U.S. Geological Survey Minerals Yearbook. N.p.: n.p., 2007. 13.8-13.10. Print.</ref> 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.<ref name="Franz">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.</ref><ref>Bonazzi, P., et al. "Karlite: Crystal Structure and Composition." Neues Jahrbuch für Mineralogie, Monatshefte (1986): 253-262. Print.</ref>

==References== {{Reflist}}

Category:Borate minerals Category:Magnesium minerals Category:Orthorhombic minerals Category:Minerals in space group 19 Category:Borate chlorides