Sterlinghillite, a New Hydrated Manganese Arsenate Mineral from Ogdensburg, New Jersey

American Mineralogist, Volume 66, pages Ig2-1g4, lggl

Sterlinghillite, a new hydratedmanganese arsenate mineral from Ogdensburg,New Jersey

Ppre J. DUNN Department of Mineral Sciences,Smithsonian Institution Washington, D. C. 20560

Abstract

Sterlinghillite is a new manganesearsenate hydrate mineral from the Sterling Hiit mine, Ogdensburg,Sussex County, New Jersey.Microprobe analysisyields MnO 39.5, FeO 0.2, MgO 0.1, ZnO 2.9, AsrO,44.7weight percent,together with water by difference12.6 percent. The tentative formula is Mnr(AsOo)2'4H2O. Sterlinghillite is white to light pink, occurs in 0.1 mm clustersof micron-sizedcrystals on loellingite-franklinite-willemite-calcite ore, and may have formed by the decompositionof loellingite. There are no crystals suitable for singlercrystalstudies. The strongestlines in the X-ray diffraction pattern are: ll.l2 (100), 3.209(100), 2.751 (60),2.848 (40), 2.880 (40), 3.692 (30), and 6.39(30). Sterlinghillite is named for the locality. The mineral is very rare and only one specimenwith a few milligrams of material has been found.

Introduction vergent angle of the crystalsin the clusterswas ob- This new mineral was called to my attention by served.The secondhabit of sterlinghillite is that of Mr. Fred Parker of South River, New Jersey.It was tiny hemisphericalclusters of platy crystals(Fig. l). found by a miner in the Sterling Hill mine and was The crystalshave a distinctly platy morphology and reportedto comefrom the 340 foot level of the mine. appear to be randomly intergrown. The extremely The new speciesand the name were approvedby the small clustersize (0.1 mm) precludedthe determina- Commissionon New Minerals and Mineral Names, tion of some of the physical and optical properties. IMA, prior to publication. Type material is preserved The paucity ofparagenetical data precludesany de- at the SmithsonianInstitution under catalog finitive statementon the formation of sterlinghillite, # NMNH 14'7269.The name is for the locality, one but the oxidation of loellingite in the presenceof of the most remarkablemineral depositson earth. manganese-bearingsolutions provides a ready mech- anism. Occurrence Chemistry Sterlinghillite is from the Sterling Hill mine, Og- densburg,Sussex County, New Jersey.Apart from its Sterlinghillite was chemically analyzed.with an reported occurrenceat the 340'level, no additional ARL-sEMe electron microprobe utilizing an oper- information is available on the geologicsetting. The ating voltage of 15 kV and a beam current of 0.15 only parageneticalinformation available is that ob- pA. The standardsused were olivenite for As, man- servedon the one known specimen.Sterlinghillite oc- ganite for Mn, zincite for Zn, and hornblendefor Fe curs on seamsin a franklinite-sphaleriteore which is and Mg. The data were correctedusing a modified in contact with a probable seam of loellingite and version of the MAGIC-4 program. A microprobe calcite. Sterlinghillite occurs in two habits on the scan indicated the absenceof any additional ele- type specimen;both habits are on seam surfaces. ments with atomic number greater than ten. Ster- Sterlinghilliteappears to be the last mineral to form. linghillite is easily soluble in dilute nitric or hydro- In one of these habits, sterlinghillite occurs as bun- chloric acids.It is chemicallyhomogeneous over l0trr dles of very soft pearly crystalswhich at first glance beamspots. No detectabledifferences were noted be- resemblesome clusters of laumontite. These clusters tween the two habits of sterlinghillite; they have are rather sparseon the specimenwith a total weight identical compositions.The resultant analysisis pre- of only severalmilligrams. No constancyof the di- sentedin Table L N03-W4X/8r/0102-0t82$02.00 182 DUNN: STERLINGHILLITE 183

Fig. I Tabular randomly oriented crystalsof sterlinghillite (1200x).

The analysisyields a ratio of Iuf* cations:As of for the direct or indirect determinationof water and 3:2 and suggeststhat the formula of sterlinghillite is the water contentmust be inferred by difference.The Mn,(AsOn), ' 4HrO. There is too little sterlinghillite absenceof single-crystaldata precludes the calcu- lation of unit-cell contents and thus the given for- Table L Microprobe analysisof sterlinghillite mula must be consideredquite tentative.The general

Mn3(As04)24H20 Sterlinghi'ilite formula i4*[(As,P) Oo],'4HrO is commonto many (theoreticalwt. Z) (wt %) species;among these are switzerite, Mn.(POo), 1"1n0 4l 35 395 4HrO; hopeite and parahopeite,Znr(POo)' ' 4HrO; Fe0 o2 and ludlamite, Fe.(POo),' 4HrO. However,the X-ray 14S0 0t powder diffraction data (Table 2) are markedly dif- 2ilO 2.9 ferent for sterlinghillitein both d valuesand the gen- As^0. 44.66 447 eral configurationofthe pattern, and strongly suggest

H^0 I 3.99 l2 6* that sterlinghillite has no structural relationship to

100.00 r00 00 theseminerals with similar atomic ratios and water content. There are no single crystalsof sterlinghillite large * water deternined by difference due to paucity of material. enoughfor single-crystalstudy. Repeatedattempts to Accuracy of data : plus or minus three percent of the amount present find suitablecrvstals were unsuccessful. I84 DUNN: STERLINGHILLIT:E

Table 2. X-ray powder diffraction data for sterlinghillit€ Physical and optical properties Sterlinghillite occursas white to light pink aggre- dR oR I/ 1o gateswhich have a white streak.The hardnessis esti- 'r00 mated as 3 (Mohs). There perfect t1.12 2.217 2 is one cleavage, 6.39 30 2.171 2 parallel to the direction of elongationof the lath-like 6,|l 2 2 049 2 crystals.The luster is silky on fracture and cleavage 5.50 2 1.975 5 't0 strfaces and dull to silky on external crystal faces. 5.0'l I .939 5 The density,measured with heavy-liquid techniques, 4.73 l0 I .855 5 'l is 2.95 g/cm3, but this measuredvalue may be low 3.960 2 . 843 t0 3.692 30 i.757 2 due to the highly porousnature of the aggregate(Fig. 3.209 100 1.714 5 l). Sterlinghillite doesnot fluorescein ultraviolet ra- 2.880 40 1.704 10 diation and there is no phosphorescence.Optically, 2.848 40 1.672 5 sterlinghillite is anisotropic with wavy but inclined 2.814 5 1.662 5 extinction.The very poor quality of the crystalspre- 2.751 60 1.604 2 cluded some optical measurements.The refractive 2.629 10 1.583 2 q.: : +0.003). 2.603 t0 I .553 2 indicesare 1.656and y 1.671(both 2.553 2 1.487 2 All crystalsshowed wavy extinction. 2.465 t0 1.447 ? 'I 2.341 2 .412 t0 Acknowledgments 2.298 2 The author is indebtedto Dr. Donald Peacorfor assistancewith the evaluationof the absenceof workable single crystals,and to 'l'l4.6 0ata obtainedwith a polycrystalline samplein a Gandolfi mm Dr. EugeneFoord for a critical reading of the manuscript. Mr. camerautilizing nickel-filtered CuKoX-radiation, and NBSsilicon Richard Johnsonand Mr. Frank Walkup preparedpolished sec- as an internal standard. tions. Mr. CharlesObermeyer provided assistancewith the microprobe.