Hardystonite



Hardystonite is a calcium zinc silicate of the melilite group. Representative analyses show that there is very limited solid solution towards melilite. Also evident is the small but ubiquitous Pb content. Hardystonite is, together with esperite, an original host for Pb in the primary ores. Bauer found 3.61 wt. % Pb in one specimen, but most have PbO values less than 1.8 wt. %. Ries and Bowen (1922) checked for native lead in thin section and found none. Lead was quite deleterious to the refining processes used by the New Jersey Zinc Company. Accordingly, it was carefully monitored, both by the manual extraction of Pb-containing minerals at the picking table and by constant sampling and chemical analysis of ores.
Hardystonite was first described from Franklin by Wolff (1899a) and Wolff and Melczer (1900). Ries and Bowen (1922) reported it occurring mainly in the northern end of the orebody. Modem microprobe analyses and a brief discussion of textural relations with esperite were given by Dunn (1985b). In spite of these works, the petrographic and genetical relations for hardystonite are little studied. Hardystonite is a common mineral at Franklin, and is second only to willemite as the most abundant zinc silicate mineral here. It has not been reported from Sterling Hill.
The crystal structure was described by Warren and Trautz (1930) and was refined by Louisnathan (1969), who described it as consisting of [Zn2Si2O7] sheets within which the nature of the bonding is dominantly covalent, with the adjacent sheets being held together by Ca2+ ions.
Although massive material is predominant, crystals of hardystonite up to at least 9 cm have been found; most are 1-2 cm in size. Such elongate crystals are slightly resorbed and have not been measured; their morphology is unknown. These crystals occur for the most part in calcite; some occur in willemite; all are rock-locked; and none have been found growing free in vugs. Hardystonite is white to gray to light pink, but may be light yellow from included zincite (Ries and Bowen, 1922). It has a distinctly greasy to vitreous luster and a density of 3.39-3.44 g/cm3 (Palache (1935). Cleavage is perfect and imperfect on; the resultant crystal fragments can have a rectangular appearance. Exsolution textures are unknown, but late-stage willemite commonly permeates the cleavage traces, giving an apparent "exsolution" appearance seen under ultraviolet.
The fluorescence in ultraviolet is bluish-violet to violet to violetish-blue in shortwave and longwave; see Newsome (1978) for details. In general, under the electron microprobe beam, the intensity of the cathodoluminescence is proportional to the Pb-content, being stronger with increasing Pb. Most hardystonite is easily distinguished by its fluorescence in ultraviolet.
Hardystonite was found in abundance in the Franklin Mine, but not even as traces at Sterling Hill: an enigma that stands unaddressed. It occurred on a large scale, as a high-temperature primary mineral, in part a reactant between calcite-bearing ore and non-calcite-bearing ore. It occurred mostly in the northern end of the deposit, as deep as the 1150 level, and also in the south end on the 600 and 800 levels, in addition to many other occurrences. Zones of hardystonite several feet (0.6 meters) across were not uncommon. It occurs in a large number of assemblages associated with a great many minerals. Foremost among these are franklinite, willemite, and calcite; zincite and esperite are also associated, albeit less abundantly.
Hardystonite is a common component of symplectites, occurring intergrown with tephroite. Most franklinite occurring within hardystonite is rimmed by reactant willemite; zincite is not so rimmed. Hardystonite also occurs in veins in willemite-franklinite ore, commonly with calcite, and sometimes occurs as a reactant where willemite-rich veins form in calcite.
Hardystonite is common to many assemblages which have Ca-Zn-Si bulk compositions. They are too numerous to list here. Of particular interest is the association of hardystonite with esperite, willemite, and franklinite, with sparse calcite (Dunn, 1985b). Esperite replaces hardystonite along cleavage traces, and willemite, hodgkinsonite, and clinohedrite form at the feathery intergrowth of esperite and hardystonite. Such assemblages are prized as fluorescent specimens. Hardystonite also occurs in banded granular ore with franklinite, willemite, and rhodonite.
Hardystonite is readily altered by hydration to clinohedrite. The replacement is commonly partial, creating thin films on open fracture surfaces. However, it may be extensive and nearly complete. In the assemblage which serves as host for glaucochroite and cuspidine crystals, hardystonite has been almost wholly replaced by clinohedrite. Not all clinohedrite occurs in this manner. Hardystonite alters surficially to a brown rind. (Dunn, 1995)


 Location Found: Franklin (Type Locality)
     
 
 Year Discovered: 1899
     
 Formula: Ca2Zn(Si2O7)
 Essential Elements: Calcium, Oxygen, Silicon, Zinc
 All Elements in Formula: Calcium, Oxygen, Silicon, Zinc
     
 IMA Status: Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
     
Fluorescent Mineral Properties

 Shortwave UV light: Violet to violet-blue
 Mid wave UV light: Violet to violet-blue
 Longwave UV light: Violet to violet-blue
     
 To find out more about this mineral at minDat's website, follow this link   Hardystonite

     
 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.411

Frondel, Clifford (1972). The minerals of Franklin and Sterling Hill, a checklist. NY.: John Willey & Sons. p.59


The Picking Table References
 PT Issue and PageDescription / Comment
V. 57, No. 2 - Fall 2016, pg. 19Fluorescent Minerals of Franklin and Sterling Hill, N.J., Part 1, Richard C. Bostwick - Hardystonite
V. 52, No. 2 - Fall 2011, pg. 7Hardystonite Fluorescence Emission Spectrum
View IssueV. 45, No. 1 - Spring 2004, pg. 11The Art of Fluorescent Mineral Photography, With Special Attention to the Minerals of Franklin and Sterling Hill Photographing the More Popular Franklin and Sterling Hill Fluorescent Minerals - Hardystonite
View IssueV. 33, No. 2 - Fall 1992, pg. 10The Check List of Franklin-Sterling Hill Fluorescent Minerals - Hardystonite (Fluorescent Info)
View IssueV. 28, No. 1 - Spring 1987, pg. 23Mineral Notes Research Reports, The Esperite Assemblage, Hardystonite
View IssueV. 18, No. 2 - September 1977, pg. 13The Fluorescent Minerals of Franklin and Sterling Hill, NJ by Richard C. Bostwick - Hardystonite
View IssueV. 15, No. 2 - August 1974, pg. 9Fluorescent Corner - Hardystonite
View IssueV. 13, No. 2 - August 1972, pg. 12The Fluorescent Minerals of Franklin/Ogdensburg Area by Frank Z. Edwards - Hardystonite (Fluorescent Info)
View IssueV. 9, No. 1 - February 1968, pg. 13The Exclusive Minerals of Franklin/Ogdensburg, N.J. (as of January 1968) by Frank Z. Edwards - Hardystonite (Short Note)
     
Images

     
Hardystonite (SW FL lilac, LW FL cream), willemite, franklinite, Franklin NJHardystonite (SW FL lilac, LW FL cream), willemite, franklinite, Franklin NJ under shortwave UV Light
Hardystonite, willemite and franklinite, from Franklin, NJ. Photo by WP.
Hardystonite, willemite and franklinite, from Franklin, NJ under shortwave UV light. The hardystonite fluoresces light violet and willemite green, franklinite is non-fluorescent. Photo by WP.
Hardystonite (SW FL lilac, LW FL cream), willemite, franklinite, Franklin NJ under longwave UV Light
Hardystonite, willemite and franklinite, from Franklin, NJ under longwave UV light. The hardystonite fluoresces cream to white (uncommon) and light violet, franklinite is non-fluorescent. Photo by WP.


Hardystonite, willemite, esperite, franklinite and minor calcite from Franklin, NJHardystonite, willemite, esperite, franklinite and minor calcite from Franklin, NJ under shortwave UV Light
Hardystonite, willemite, esperite, franklinite and minor calcite from Franklin, NJ. 4 3/4" x 3 5/8". From the collection of, and photo by Robert A. Boymistruk.
Hardystonite, willemite, esperite, franklinite and minor calcite from Franklin, NJ under shortwave UV light. 4 3/4" x 3 5/8". The hardystonite fluoresces violet, willemite green, esperite yellow and calcite red-orange, the franklinite is non-fluorescent. From the collection of, and photo by Robert A. Boymistruk.


Hardystonite, clinohedrite, willemite, calcite, franklinite and zincite from Franklin, NJHardystonite, clinohedrite, willemite, calcite, franklinite and zincite from Franklin, NJ under shortwave UV Light
Hardystonite, clinohedrite, willemite, calcite, franklinite (black) and zincite (light orange brown) from Franklin, New Jersey. 5 1/4" x 3 7/8". From the collection of, and photo by Robert A. Boymistruk.
Hardystonite, clinohedrite, willemite, calcite, franklinite and zincite from Franklin, NJ under shortwave UV light. The hardystonite fluoresces violet blue, calcite red orange, willemite green and clinohedrite orange, and the franklinite is non-fluorescent. 5 1/4" x 3 7/8". From the collection of, and photo by Robert A. Boymistruk.


Hardystonite, clinohedrite, willemite, calcite, garnet and franklinite from Franklin, NJHardystonite, clinohedrite, willemite, calcite, garnet and franklinite from Franklin, NJ under shortwave UV Light
Hardystonite, clinohedrite, willemite, calcite, garnet (dark brown) and franklinite (black) from Franklin, New Jersey. 5 3/8" x 3 1/4". From the collection of, and photo by Robert A. Boymistruk.
Hardystonite, clinohedrite, willemite, calcite, garnet and franklinite from Franklin, NJ under shortwave UV light. The hardystonite fluoresces violet blue, calcite red orange, willemite green and clinohedrite orange, the garnet and franklinite are non-fluorescent. 5 3/8" x 3 1/4". From the collection of, and photo by Robert A. Boymistruk.


Hardystonite vein, willemite, calcite, and franklinite from Franklin, NJHardystonite vein, willemite, calcite, and franklinite from Franklin, NJ under shortwave UV Light
Hardystonite vein, willemite, calcite and franklinite (black) from Franklin, New Jersey. 10" x 6". Photo by WP.
Hardystonite vein, willemite, calcite, and franklinite from Franklin, NJ under shortwave UV light. The hardystonite fluoresces violet blue, calcite red orange and willemite green, the franklinite is non-fluorescent. 10" x 6". Photo by WP.







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