Holdenite is a manganese zinc arsenate silicate hydroxide mineral. Because the original analysis was performed on a mixture and the crystal structure determination (Moore and Araki, 1977b) indicated that Si was essential to the species, holdenite was reinvestigated analytically by Dunn (1981e). They conform closely to the ideal composition, with approximately 2 weight percent MgO proxying for ZnO; no holdenite has been found to be Mg-free.
Holdenite was first described from Franklin by Palache (1921) and Palache and Shannon (1927) as a manganese zinc arsenate hydrate. Their analysis was of admittedly impure material, and they dismissed the low silica component of the analysis as willemite impurities. The crystallography of holdenite was later investigated by Prewitt-Hopkins (1949), but her space group was subsequently corrected by Moore and Araki (1977b). The discovery of holdenite at Sterling Hill in 1977 and again in subsequent years provided additional material for analytical studies by Dunn (1981e).
Moore and Araki (1977b) described the crystal structure and showed that Si was essential to holdenite. They described the structure as having open tetrahedral sheets of composition [Zn2SiO6(OH)2] which are further linked to AsO4 tetrahedra to form slabs of composition [Zn2As2SiO12(OH)2]; insular ZnO, tetrahedra also occur. These slabs link to Mn(O,OH) condensed octahedra to form a framework structure based on cubic close-packing of oxygens.
Holdenite crystals are up to 2-3 mm in size. Those from Franklin were depicted by Palache and Shannon (1927) and Palache (1935).
The morphology of holdenite is similar to that of kolicite. Sterling Hill crystals are commonly distorted, as shown by Dunn (1981e).
Holdenite is commonly light pink; crystals forming druses on other species may have false colors transmitted through the transparent holdenite. Holdenite has a vitreous luster. Palache and Shannon (1927) reported a poor cleavage. The density is 4.11 g/cm3 (meas.) (Prewitt-Hopkins, 1949), 4.11 g/cm3 (calc.) (Moore and Araki, 1977).
Optically, holdenite has not been restudied. There is no discernible fluorescence in ultraviolet. Holdenite is brittle, and broken crystals resemble leucophoenicite, but the higher density is diagnostic. Holdenite also resembles some hodgkinsonite; it is easily distinguished by hodgkinsonite's lower indices of refraction. Because holdenite, a pink glassy mineral, is easily confused with leucophoenicite at Franklin or hodgkinsonite at either locality, specimens of holdenite may possibly be mislabeled in systematic collections, as first suggested by Albanese (1955), but [Dunn’s] search for such mislabeled material has been fruitless.
Holdenite was originally found at Franklin. It is a mineral of the secondary veins, and it remained a very rare species until the discovery of Sterling Hill material by Fred Parker in 1977. The Sterling Hill occurrence, which provided hundreds of specimens, was between the 1200 and 1300 levels in the central zincite zone. Like Franklin material, holdenite from Sterling Hill also accompanies slickensides and is also found with secondary willemite as banded vein-fillings. In some specimens, holdenite occurs within the ore adjacent to veins and locally may compose up to 10% by volume. Within such assemblages, kraisslite is present as thin plates. Sterling Hill holdenite is invariably pink. Holdenite in association with kolicite was noted by Dunn et al. (1979b). (Dunn, 1995)

 Location Found: Franklin (Type Locality) and Ogdensburg, unique to Franklin/Ogdensburg area
 Year Discovered: 1921
 Formula: (Mn2+,Mg)6Zn3(AsO4)2(SiO4)(OH)8
 Essential Elements: Arsenic, Hydrogen, Manganese, Oxygen, Silicon, Zinc
 All Elements in Formula: Arsenic, Hydrogen, Magnesium, Manganese, Oxygen, Silicon, Zinc
 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   Holdenite

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.376

Frondel, Clifford (1972). The minerals of Franklin and Sterling Hill, a checklist. NY.: John Willey & Sons. p.61

The Picking Table References
 PT Issue and PageDescription / Comment
V. 57, No. 2 - Fall 2016, pg. 20Fluorescent Minerals of Franklin and Sterling Hill, N.J., Part 1, Richard C. Bostwick - Holdenite
View IssueV. 37, No. 1 - Spring 1996, pg. 19Closest-Packed Mineral Structures of Franklin-Ogdensburg: Kepler's Gift of the Snowflake, Part two of two parts, Paul B. Moore - Holdenite
View IssueV. 24, No. 1 - Spring 1983, pg. 6Recent Mineral Occurrences at Sterling Hill, Stephen B. Sanford, Holdenite
View IssueV. 23, No. 1 - Spring 1982, pg. 12Mineral Notes Research Reports, Holdenite
View IssueV. 9, No. 1 - February 1968, pg. 14The Exclusive Minerals of Franklin/Ogdensburg, N.J. (as of January 1968) by Frank Z. Edwards - Holdenite (Short Note)

Holdenite, willemite, franklinite and calcite from Sterling Hill Mine, Ogdensburg, NJ
Holdenite (pink), willemite (reddish brown), franklinite (black) and calcite (white to light tan) from the Sterling Hill Mine, Ogdensburg, NJ. 3 5/8" x 2 1/4". From the collection of, and photo by Robert A. Boymistruk.

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