DIOPSIDE

Diopside is a calcium magnesium silicate mineral of the pyroxene group and is the preferred host for Mg in the calcium-silicate assemblages. The name diopside is best applied only to light-colored specimens. Diopside from the quarries in the Franklin Marble is of near end-member composition, but the platy material from the orebodies contains much Mn, Zn, and Fe and grades into aegirine and augite. There is much variation in composition, and numerous solid solution series extend toward johannsenite, hedenbergite, petedunnite, aegirine, and augite.
Diopside is the dominant clinopyroxene at both Franklin and Sterling Hill; in addition, it is found in moderate abundance in the marble quarries. Because the relations among the clinopyroxenes were not well understood at the time of early investigations, a number of superfluous names were used. The names schefferite, white schefferite, and zinc-schefferite, when applied to white or light brown specimens, refer to material that is diopside. Schefferite was so-called because of its physical and compositional similarity to the original Swedish material (Palache, 1910, 1935). Zincschefferite was described by Wolff and Melczer (1900), who analyzed material previously examined by Hillebrand (1900). These names were adopted by Palache (1935). For dark brown or brownish-green material, see the remarks under augite.
Diopside from the Franklin and Sterling Hill orebodies is white to light brown; it may be colorless in the Franklin Marble. It has a density of 3.2-3.4 g/cm³, a vitreous luster, and a prominent parting. In ultraviolet, near-end-member diopside from the Franklin Marble has a blue fluorescence in shortwave and a light yellow fluorescence in longwave. Most samples from the orebody have no discernible fluorescence. It is easily distinguished from andradite on the basis of its common parting.
Diopside is common to many of the high-temperature assemblages of the calcium-silicate units at Franklin and Sterling Hill. The more common associated minerals are franklinite, willemite, andradite, and calcite. Rhodonite, bustamite, hardystonite, apatite, and secondary clinohedrite are also associated, as are numerous other minerals. The assemblages for diopside have not been examined in detail and the petrographic relations are unstudied.
At Sterling Hill, diopside is associated with gahnite and calcite. Dark brown material with prominent parting, likely diopside or augite, has been found on the 1300 and 1400 levels at Sterling Hill, associated with calcite, franklinite, rhodonite, andradite, and willemite. Large 1.5 cm unanalyzed crystals are associated with hornblende. Reilly (1983) reported diopside-augite with exsolved rhodonite from Sterling Hill drill-hole #124, 19 feet from its beginning on the 340 level.
In the Franklin Marble, diopside is associated with tremolite, corundum, and numerous other silicates found in the quarries. (Dunn, 1995)

Location Found:

Franklin and Ogdensburg

Formula:

CaMgSi₂O₆

Essential Elements:

Calcium, Magnesium, Oxygen, Silicon

All Elements in Formula:

Calcium, Magnesium, Oxygen, Silicon

IMA Status:

Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"

Fluorescent Mineral Properties

Shortwave UV light:

Fairly bright pale blue

Mid wave UV light:

Weak pale orange-yellow

Longwave UV light:

Weak pale orange-yellow

Additional Information:

Fluoresces weakest longwave

To find out more about this mineral at minDat's website, follow this link Diopside

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.432

Frondel, Clifford (1972). The minerals of Franklin and Sterling Hill, a checklist. NY.: John Willey & Sons. p.53

The Picking Table References

	PT Issue and Page	Description / Comment
	V. 64, No. 1 – Spring 2023, pg. 14	Analyses of Clinopyroxenes From Franklin and Ogdensburg, New Jersey, U.S.A., Harold Moritz and Frank M. Craig
View Issue	V. 57, No. 2 - Fall 2016, pg. 16	Fluorescent Minerals of Franklin and Sterling Hill, N.J., Part 1, Richard C. Bostwick - Diopside
View Issue	V. 45, No. 1 - Spring 2004, pg. 10	The 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 - Diopside
View Issue	V. 33, No. 2 - Fall 1992, pg. 10	The Check List of Franklin-Sterling Hill Fluorescent Minerals - Diopside (Fluorescent Info)
View Issue	V. 30, No. 1 - Spring 1989, pg. 8	The Epidote-Pyroxene-Fluorapophyllite Assemblage in the Franklin Mine at Franklin, New Jersey, Philip P. Betancourt, Diopside (small description)
View Issue	V. 18, No. 1 - March 1977, pg. 24	The Fluorescent Minerals of Franklin and Sterling Hill, NJ by Richard C. Bostwick - Diopside
View Issue	V. 13, No. 2 - August 1972, pg. 12	The Fluorescent Minerals of Franklin/Ogdensburg Area by Frank Z. Edwards - Diopside (Fluorescent Info)

Images


Diopside (gray) and phlogopite mica (light brown) in franklin marble, Franklin NJ. Photo by JVF		Diopside and phlogopite mica in franklin marble, Franklin NJ under shortwave UV light. The diopside fluoresces light blue and phlogopite straw yellow, the marble is non-fluorescent.


Diopside "zinc schefferite" (tan to brown), willemite (white to light green) with minor franklinite (black) and rhodonite (pink), from Franklin, NJ. 5" x 2 1/2". Photo by WP.		Diopside "zinc schefferite", willemite with minor franklinite and rhodonite, from Franklin, NJ under shortwave UV light. The willemite fluoresces green, the diopside, franklinite and rhodonite are non-fluorescent 5" x 2 1/2". Photo by WP.

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