Hardystonite

(repeating unit)Ca2ZnSi2O7IMA symbolHdy[1]Strunz classification9.BB.10Dana classification55.4.2.2Crystal systemTetragonalCrystal classScalenohedral (42m)
H-M symbol: (4 2m)Space groupP421mUnit cella = 7.8287(16) Å
c = 5.0140(2) Å; Z = 2IdentificationColorLight brownish white, pale greyish-white, very pale pinkCrystal habitMassive granularCleavage[001] good, [100] and [110] fairTenacityBrittleMohs scale hardness3–4LusterVitreous, resinous, greasy, dullDiaphaneityTransparent to translucentSpecific gravity3.396–3.443Optical propertiesUniaxial (−)Refractive indexnω = 1.672 nε = 1.661Ultraviolet fluorescencePurple to violet blue in short wave ultraviolet lightAlters toHydrothermal alteration to clinohedriteReferences[2][3][4]

Hardystonite is a rare calcium zinc silicate mineral first described from the Franklin, New Jersey, U.S. zinc deposits.[2] It often contains lead, which was detrimental to the zinc smelting process, so it was not a useful ore mineral.[5] Like many of the famous Franklin minerals, hardystonite responds to short wave ultraviolet (254 nm wavelength) light, emitting a fluorescence from dark purple to bright violet blue. In daylight, it is white to gray to light pink in color, sometimes with a vitreous or greasy luster. It is very rarely found as well formed crystals, and these are usually rectangular in appearance and rock-locked.[6]

Hardystonite in plain light, same sample as in fluorescent light image above right

Hardystonite has a chemical composition of Ca2ZnSi2O7. It is frequently found with willemite (fluoresces green), calcite (fluoresces red), and clinohedrite (fluoresces orange). Hardystonite can be found altered to clinohedrite CaZn(SiO4)·H2O through direct hydrothermal alteration.[6] Other minerals often associated with hardystonite are franklinite, diopside, andradite garnet, and esperite (fluoresces yellow).

It was first described in 1899 by J.E. Wolff, when the New Jersey Zinc Company mines were located in what was called Franklin Furnace, in Hardyston Township, New Jersey.[6]

References

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b http://www.mindat.org/min-1818.html Mindat
  3. ^ http://www.webmineral.com/data/Hardystonite.shtml Webmineral data
  4. ^ Handbook of Mineralogy
  5. ^ Palache, Charles (1935). "The minerals of Franklin and Sterling Hill, Sussex County, New Jersey" (PDF). Geological Survey Professional Paper. 180: 122–123. doi:10.3133/PP180. ISSN 0096-0446. Wikidata Q58144929.
  6. ^ a b c Dunn, Pete J. Franklin and Sterling Hill, New Jersey: the world's most magnificent mineral deposits. Dr. Pete J. Dunn, 2004.
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