Alleghanyite



Alleghanyite is a manganese silicate hydroxide mineral of the manganese-humite group; most local samples have magnesium and zinc substituting for manganese. Samples from Sterling Hill are markedly higher in Mg than those from Franklin, reflecting the generally higher concentration of Mg in Sterling Hill silicates.
Of particular interest, in all analyses of Franklin alleghanyite is the invariance of Zn. Zinc is a common substituent in silicate phases at Franklin and Sterling Hill, and its presence is expected. However, in no studied local material is there an alleghanyite specimen without Zn, nor is there one with Zn in excess of relatively invariant amounts. Some of these alleghanyites coexist with zincite (ZnO), but the majority have only willemite as an associated Zn-phase. Fluorine is common in most alleghanyite, averaging 40% of the (OH) site in magnesian material and generally decreasing with increasing Mn content.
Alleghanyite was first noted from Franklin and Sterling Hill by Cook (1969) who cleared up part of the confusion arising from earlier morphological studies. White and Hyde (1982b) examined several Franklin samples using TEM techniques; although they found several phases associated with alleghanyite (chiefly leucophoenicite and sonolite), these minerals were present as fragments and not as intergrowths.
Alleghanyite occurs as dark-brown massive material and as euhedral light-brown 1-3 mm crystals in veins. Morphologically, the crystals were found to be untwinned. For such crystals the luster is vitreous; cleavage is absent; and the density is 3.75 g/cm3. There is no discernible fluorescence in ultraviolet. Alleghanyite, like all the Mn-humites, is best distinguished from related species using X-ray methods.
Alleghanyite occurs at both Franklin and Sterling Hill. At Franklin, there are few known assemblages. The best-preserved of these was identified by Palache (1928) as leucophoenicite. This material consists of veins up to 3 cm thick, associated with calcite, franklinite and sussexite. The bulk of this material consists of massive brown alleghanyite which forms euhedral crystals on exposed surfaces. Leucophoenicite is also present, both as epitaxial overgrowths on the terminations of alleghanyite crystals and as apparently randomly oriented euhedra, perhaps of a subsequent growth period. Although alleghanyite has been found on a few Franklin specimens from other assemblages, it is uncommon.
At Sterling Hill, alleghanyite occurs rarely as euhedral 1-2 mm crystals and thin seams which crosscut the ore. In hydrothermal veinlets, these crystals may accompany arsenate species, such as kolicite, holdenite, magnussonite, adelite, kraisslite, chlorophoenicite, and others. Commonly associated with alleghanyite are franklinite, willemite, barite, and carbonates, all of secondary recrystallization. The observed species all occur on willemite/franklinite ore which contains abundant calcite. Some of the best samples were found in the late 1970's, and numerous well-studied specimens are in the Harvard collection. (Dunn, 1995)


 Location Found: Franklin and Ogdensburg
     
 
 Year Discovered: 1932
     
 Formula: Mn52+(SiO4)2(OH)2
 Essential Elements: Hydrogen, Manganese, Oxygen, Silicon
 All Elements in Formula: Hydrogen, Manganese, Oxygen, Silicon
     
 IMA Status: Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
     
     
 To find out more about this mineral at minDat's website, follow this link   Alleghanyite

     
 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.348

Frondel, Clifford (1972). The minerals of Franklin and Sterling Hill, a checklist. NY.: John Willey & Sons. p.40


The Picking Table References
 PT Issue and PageDescription / Comment
View IssueV. 27 No. 2 - Fall 1986, pg. 19A Highly Magnesian Alleghanyite From Sterling Hill, New Jersey
View IssueV. 27 No. 2 - Fall 1986, pg. 28Mineral Notes Research Reports, Magnesian Alleghanyite
View IssueV. 27, No. 1 - Spring 1986, pg. 7Mineral Notes Research Reports, Alleghanyite
View IssueV. 24, No. 1 - Spring 1983, pg. 4Recent Mineral Occurrences at Sterling Hill, Stephen B. Sanford, Alleghanyite
View IssueV. 15, No. 1 - February 1974, pg. 10Research Reports - Alleghanyite (small article)
View IssueV. 11, No. 1 - February 1970, pg. 6Mineral Data - Sonolite, Alleghanyite, Leucophoenicite
View IssueV. 11, No. 1 - February 1970, pg. 8Mineral Data - Alleghanyite
     
Images

     
Alleghanyite crystals, rhodochrosite, hetaerolite crystals and chlorophoenicite crystals from Franklin, NJ
Alleghanyite crystals (dark red), rhodochrosite (pink), hetaerolite crystals (black) and chlorophoenicite crystals (white needles) from Franklin, NJ. From the collection of, and photo by Robert A. Boymistruk.







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