Wallkilldellite is a calcium manganese arsenate hydroxide hydrate mineral and is isostructural with kittatinnyite.
Wallkilldellite was described by Dunn and Peacor (1983a) from Sterling Hill; it has not been found at Franklin.
Wallkilldellite occurs as flattened radial clusters of dark red, platy, 0.1 mm crystals with perfect cleavage and vitreous luster. The density is 2.85 g/cm3 (meas.), 2.90 g/cm3 (calc.). It is slightly similar to mcgovernite, kraisslite, and the unnamed Fe+ analogue of hematolite, but is much redder than these minerals. It is best differentiated using X-ray methods.
Wallkilldellite was found in approximately 1974 at Sterling Hill near the 340 level. The matrix is franklinite/willemite/calcite ore, the surface of which is coated with carbonates, followed by a cuproan, manganoan adamite which is present as a light yellow-green fibrous coating.
Wallkilldellite is the last mineral to form in this assemblage, occurring as 0.5 mm aggregates of platy crystals. It is quite rare. See discussion for kittatinnyite. (Dunn, 1995)

 Location Found: Ogdensburg (Type Locality)
 Year Discovered: 1982
 Formula: Ca2Mn32+(AsO4)2(OH)4 · 9H2O
 Essential Elements: Arsenic, Calcium, Hydrogen, Manganese, Oxygen
 All Elements in Formula: Arsenic, Calcium, Hydrogen, Manganese, Oxygen
 IMA Status: Approved 1982
 To find out more about this mineral at minDat's website, follow this link   Wallkilldellite

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.684

The Picking Table References
 PT Issue and PageDescription / Comment
View IssueV. 25 No. 1 - Spring 1984, pg. 8Mineral Notes Research Reports, Wallkilldellite
View IssueV. 24 No. 2 - Fall 1983, pg. 8Mineral Notes New To Science, Wallkilldellite
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