Silicates are given first; they are, with oxides, the most important minerals found locally. The silicate mineral groups are generally presented in the traditional manner, in order of increasing silicate polymerization; nesosilicates precede sorosilicates and so on. The general framework of the Dana system is employed, but not a slavish devotion to its details.
In general, minerals belonging to recognized structural groups are presented as group units. Thus, among the nesosilicates, the olivines, the humites, the manganese-humites, and the garnets are presented in groups, and the other nesosilicates are given in alphabetical order; among inosilicates, the pyroxenes, pyroxenoids, and amphiboles are presented in groups, and so on. The minerals in each section are given in alphabetical order and, excepting the olivine-related minerals, those within groups are separately alphabetized; numerous distinctions are permitted by this flexible approach.
This study is intended as an adjunct to that of Palache (1935), and much data given by him, especially morphological data, is not repeated. Two distinct formats for descriptions are used in this study. The description of species for which little data or few specimens exist, or of species which may be of trivial significance locally, is given in an abbreviated format. For all others, the preponderance, a more structured format is employed, as described below.
The general order of presentation for each species is: heading, introduction, crystal structure, description, composition, occurrence and paragenesis, and the derivation of the mineral name if the species was first described from these deposits. Quantitative data are given only if they have been determined on material from Franklin or Sterling Hill. References to studies providing such data are generally cited but once per section to avoid clutter and excessive length. The discussions of individual species is intentionally uneven; emphasis is given to the unusual minerals. For a very few minerals, which are very important locally, the given description is abbreviated and more than a bit inadequate; it would take individual volumes to fully describe the mineralogy of willemite, franklinite, and zincite.
The heading gives the correct species name, formula, crystal system, space group, unit-cell parameters, and Z, the number of formula units per unit cell.
The introduction section gives the original citation, a limited history, relevant or most significant references to prior studies, synonyms, any redefinitions, and a citation of the crystal structure if it is not given herein and if it was described or refined using local material. Also noted here is the specific occurrence of each mineral: at Franklin or Sterling Hill, or in the Franklin Marble, in the magnetite deposits, in the local country rock, or in several of these environments.
The crystal structure section contains an abbreviated and brief general description of the crystal structure of the mineral. However, this is done only for the rare and unusual minerals, and does not include the very well-known structure types. Particular emphasis is placed on zincosilicates, arsenosilicates, lead silicates, and zinc minerals in general. In most cases, these structures were determined using local material. Many silicates form zincosilicate linkages as cited in the text. Discussions of the crystal structures of some local minerals were given by Moore (1994, 1995).
The description section commonly provides the general aspect, aggregate type, and crystal habit. Crystal forms are given for recently described species; those of long established species are given by Palache (1935). Crystal drawings from Palache (1935) have been included here without the crystallographic data. Other crystal drawings, by Palache in subsequent years and by other writers, are presented where appropriate within the text. The drawings of tephroite, willemite, celestine, and calcite given by Gordon (1922) and drawings of datolite and hodgkinsonite given by Gordon (1923b) are not included in this volume. This section also includes some principal physical properties (color, luster, cleavage, and observed density). The optical data and density data are obtained almost wholly from the cited literature; only some have been verified. The fluorescence in ultraviolet, subjectively observed using common, commercially available, multi- wavelength lamps, is given only in general terms; no detailed or wavelength-specific studies of fluorescence have been done by the writer.
The composition section gives the chemical composition of the mineral in words, the relationship to other species or groups, and chemical analyses, including some from the literature and favoring modern microprobe analyses. This section contains much previously unpublished chemical data. Some of the problems of older analyses are addressed, together with the extant solid-solution evidence and relations. All analyses not cited by references are the responsibility of the writer; such analyses were all performed using electron-microprobe methods.
The occurrence and paragenesis section describes the original assemblage, the widespread or restricted occurrence of the mineral, the most important assemblages, and any special assemblages so noted for their uniqueness or historical significance. Paragenesis, the order of crystallization, is addressed if known, as are alterations and pseudomorphs. Unless a species was first found at Sterling Hill, occurrences from Franklin are noted first, followed by those from Sterling Hill, then from the Franklin Marble, and lastly from other environments. In general, with exceptions, some of the occurrences described by Palache (1935) are not included, except where new observations are available. The descriptions of Palache (1935) and Hendricks (1960) are superb and are required reading for the serious student of Franklin and Sterling Hill.
The name derivation is given only for minerals described initially from Franklin or Sterling Hill.
Specimen numbers, in unprefixed digits or prefixed by R, B, and C, are those of the National Museum of Natural History (Smithsonian Institution). Other prefixes include those of the Franklin Mineral Museum (FMM), Harvard University (HU), the American Museum of Natural History (AMNH), and the Academy of Natural Sciences of Philadelphia (ANSP). All other names or prefixed letters refer to non-institutional collections.
A little less than half of the species occurring locally are silicates. The preponderance of them occur in the calcium-silicate units of the Franklin orebody (Frondel and Baum, 1974). A lesser number occur in the pyroxene zones at Sterling Hill (Metsger et al., 1958).
The dominant Zn-Mn-Fe-Ca-Si-O chemical composition of the deposits is largely reflected in the silicate assemblages. Zinc, manganese, and calcium silicates are predominant, and their occurrences reflect the greater complexity and geochemical diversity of the Franklin deposit, relative to that at Sterling Hill. To a first approximation, Franklin has twice the number of zinc and manganese silicates and approximately thrice as many calcium silicates as Sterling Hill.
The given classification of the local silicates as zinc silicates, manganese silicates, calcium silicates, etc., is an intentionally forced one, created only to be a useful illustrative tool. A number of these minerals have several of these components; for examples, in addition to Si, franklinfurnaceite contains Ca, Mn, Zn, and Fe3+, and samfowlerite contains Ca, Mn, Zn, and Be.
Species are listed below only if the cited component (Mn, Zn, Fe, or Ca) is essential to the species; thus, species like rhodonite and leucophoenicite, which locally are almost always calcium-bearing, but do not have essential calcium, are not included among the calcium silicates. Because they do not reflect the unique aspects of the orebodies, magnesium silicates are not listed. The listed species are given with a designation that they are known to occur at Franklin (F), at Sterling Hill (SH), or at both deposits (F/SH).
Zinc silicates are common to both deposits, but more common at Franklin. Over 20 zinc silicate minerals occur here, and most occur at Franklin; about half occur at Sterling Hill. Willemite is the dominant zinc silicate at both deposits. Substantial amounts of hardystonite were found at Franklin, but not a trace at Sterling Hill. Although not containing essential zinc, rhodonite, tephroite, pyroxenes, amphiboles, and micas are minor but volumetrically significant hosts for Zn.
Zinc silicate minerals from Franklin and Sterling Hill
Manganese silicates are among the most abundant silicates at these deposits; over 40 are known to occur locally. Of these, most occur at Franklin, and about half occur at Sterling Hill. At Franklin, tephroite and the manganese humites are the dominant manganese silicates in the ore units. Tephroite also exists in the silicate units and, together with bustamite, rhodonite, and glaucochroite, hosts much of the manganese present in silicates. Sterling Hill silicate assemblages are generally Mn- and Mg-rich. Spessartine, tephroite, rhodonite, and pyroxenes, among others, are major hosts for Mn. The manganese silicates (gerstmannite, kraisslite, manganpyrosmalite, and mcgovernite) which occur at Sterling Hill, but not at Franklin, are vein minerals.
Manganese silicate minerals from Franklin and Sterling Hill
The formation of a high-temperature silicate orebody in a highly calcic environment has generated a great number of Ca-bearing silicate minerals. There are over 60 calcium silicate minerals found locally. Of these most are known from Franklin; about a third are known from Sterling Hill.
The local calcium silicates lacking Pb, Mn, or Zn have not been subjected to much scientific investigation. The dominant calcium silicates at Franklin are andradite, diopside, hardystonite, bustamite, actinolite, and a number of pyroxenes and pyroxenoids. Calcium is pervasive in most Franklin assemblages, and significant amounts are found in rhodonite, leucophoenicite, vesuvianite, wollastonite, grossular, glaucochroite, johannsenite, and many other minerals. At Sterling Hill, complex calcium silicates containing Mn and Zn are markedly less abundant; andradite is sparse relative to Franklin; and much Ca is held in various pyroxenes.
In general, excepting andradite at Franklin, silicates containing essential iron are uncommon at both deposits. There is, however, in general, more substitution of iron for Mn and Mg in silicates at Sterling Hill than at Franklin. The dominant iron silicate mineral at Franklin is andradite; minor hosts for iron are fayalite and aegirine-augite. At Sterling Hill, iron-bearing fayalite is a principal component of the black willemite zone, the micas are iron-bearing, and much iron is hosted in pyroxenes, amphiboles, and other minerals.
Iron silicate minerals from Franklin and Sterling Hill.
Magnesium is more common in Sterling Hill silicates than in those from Franklin, a relation addressed in part by Metsger et al. (1958), who proposed magnesium metasomatism as a partial cause. This prevalence extends to high-temperature phases as well as others. The dominant magnesium silicates at Franklin are diopside, augite, actinolite, and various amphiboles and pyroxenes; serpentines are common at low temperatures. At Sterling Hill, much Mg is present in silicates, particularly tephroite, manganese humites, micas, amphiboles, and pyroxenes in high-temperature assemblages, and serpentine and talc in low temperature assemblages.
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