Hydroxyapophyllite is a potassium calcium silicate hydroxide hydrate mineral. The only extant analysis is that of Bauer and Berman (1930), which yielded: SiO2 50.90, CaO 24.74, K2O 3.70, Na2O 0.42, MnO 0.47, ZnO 1.79, H2O 17.71, total = 99.73
wt. %, indicating it is close to the (OH) end-member of the fluorapophyllite-hydroxyapophyllite series.
Hydroxyapophyllite was first described from Franklin (as apophyllite) by Bauer and Berman (1930); it has not been studied since.
Hydroxyapophyllite occurs as 3-5 mm euhedral, lustrous, light pink to colorless crystals. The crystals radiate from nodes. Bauer's catalogue gives a measured density of 2.33 g/cm3.
Bauer's analyzed Franklin hydroxyapophyllite occurs as a mass of crystals, 6 x 10 cm in dimension, associated with minor calcite. It was reported to come from crumbly limestone (marble). A note in Bauer's catalogue indicates it was found in April 1924, on the 300 level at Franklin. (Dunn, 1995)

 Location Found: Franklin
 Year Discovered: 1978
 Formula: KCa4(Si8O20)(OH,F) · 8H2O
 Essential Elements: Calcium, Hydrogen, Oxygen, Potassium, Silicon
 All Elements in Formula: Calcium, Fluorine, Hydrogen, Oxygen, Potassium, Silicon
 IMA Status: Approved
Fluorescent Mineral Properties

 Shortwave UV light: Weak white
 Additional Information: Phosphoresces weak white
 To find out more about this mineral at minDat's website, follow this link   Hydroxyapophyllite-(K)

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.497. 'Hydroxyapophyllite'

The Picking Table References
 PT Issue and PageDescription / Comment
View IssueV. 57, No. 2 - Fall 2016, pg. 20Fluorescent Minerals of Franklin and Sterling Hill, N.J., Part 1, Richard C. Bostwick - Hydroxyapophyllite-(K)
View IssueV. 33, No. 2 - Fall 1992, pg. 11The Check List of Franklin-Sterling Hill Fluorescent Minerals - Hydroxyapophyllite (Fluorescent Info)
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