Kraisslite



Kraisslite is a ferric-iron magnesium manganese zinc arsenite arsenate silicate hydroxide mineral. The formula first proposed,
(Mn0.89Mg 0.08Fe2+0.03)24Zn4(ASO4)4(SiO4)8(OH)12, was shown by Dunn and Nelen (1980) to be incorrect. They proposed Fe3+2Mg4Mn44Zn6(AsO3)4 (AsO4)6(SiO4)12(OH)36 as an interim formula pending structural investigation. Kraisslite is relatively invariant in chemical composition from specimen-to-specimen, indicating that the diverse array of cations is indicative of the true composition and not the effects of random solid solution.
Kraisslite was first described by Moore and Ito (1978) as a platy arsenosilicate from Sterling Hill; it has not been found at Franklin. Kraisslite was redefined by Dunn and Nelen (1980), who presented the extant formula. Although its crystal structure has not been determined, it is clearly related to those of mcgovernite, hematolite, and its unnamed Fe3+ analogue (Dunn and Peacor, 1983b).
Kraisslite occurs as hexagonal, platy crystals composed of only the pinacoid and prism; such neat crystals are rare. The preponderance of kraisslite exists as thin films and coatings of crystal aggregates on fracture surfaces; such coatings can be extensive. Much kraisslite occurs as thin foliae, commonly warped, with a reddish-brown to bronze-brown color. The hardness is between 3 and 4; and the luster is vitreous to submetallic. The density is 3.876 g/cm3 (Moore and Ito, 1978), compared with the calculated value of 3.92 g/cm3 for the formula proposed by Dunn and Nelen (1980). There is no discernible fluorescence in ultraviolet.
Kraisslite can be confused with mcgovernite, but they are distinguished by their indices of refraction. Another similar phase is the unnamed Fe3+ analogue of hematolite. In both cases, X-ray powder diffraction techniques are recommended for unambiguous identification.
Kraisslite occurs, for the most part, as thin films and lenses along fractures in the ore in the central zincite zone at Sterling Hill. Veins and lenses of kraisslite have been found up to 1 inch thick. It is not a rare mineral; much material has been found and preserved. Kraisslite is found associated consistently with zincite and also with a number of arsenate species, such as holdenite, chlorophoenicite, sarkinite, eveite, allactite, retzian-(Nd), and others. Indeed, its occurrence with a broad array of secondary minerals indicates it might be a stable entity over a broad range of conditions.
One occurrence of kraisslite warrants special mention because it occurred within the ore and not as secondary coatings. This occurrence was on the 700 level and consisted of massive segregations of kraisslite (up to 1.0 cm) within low-grade willemite-calcite-franklinite ore. Volumetrically, kraisslite may be the most abundant arsenate mineral at Sterling Hill, but it is apparently localized in occurrence, being found only below the 500 level and never in the black-willemite ore (Parker and Troy, 1982). (Dunn, 1995)


 Location Found: Ogdensburg (Type Locality), unique to Franklin/Ogdensburg area
     
 
 Year Discovered: 1977
     
 Formula: Zn3(Mn,Mg)25(Fe3+,Al)(As3+O3)2[(Si,As5+)O4]10(OH)16
 Essential Elements: Arsenic, Hydrogen, Iron, Manganese, Oxygen, Silicon, Zinc
 All Elements in Formula: Aluminum, Arsenic, Hydrogen, Iron, Magnesium, Manganese, Oxygen, Silicon, Zinc
     
 IMA Status: Approved 1977
     
     
 To find out more about this mineral at minDat's website, follow this link   Kraisslite

     
 References:
Dunn, Pete J. (1995). Franklin and Sterling Hill New Jersey: the world's most magnificent mineral deposits. Franklin, NJ.: The Franklin-Ogdensburg Mineralogical Society. p.498


The Picking Table References
 PT Issue and PageDescription / Comment
View IssueV. 22, No. 2 - September 1981, pg. 7Mineral Notes Research Reports, Kraisslite and Mcgovernite
View IssueV. 20, No. 1 - March 1979, pg. 5New Minerals - Kraisslite
     
Images

     
Kraisslite mineral coating on red willemite, calcite and franklinite, from Sterling Hill, NJ.
Kraisslite mineral coating on red willemite, calcite and franklinite, from Sterling Hill, NJ. Photo by JVF.


Kraisslite on franklinite and willemite from Sterling Hill, NJ
Kraisslite mineral coating (brass colored) on franklinite (black) and willemite (light red) from Sterling Hill, NJ. 4" x 3 1/2" From the collection of Gary Moldovany, photo by WP.







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