Colorless gemmy willhendersonite crystals, a rare mineral at Eifel (Rother Kopf, Roth, Eifel Mountains, Germany), associated to off-white uncommon gismondite globular aggregates. Willhendersonite is a marker for other extremely rare species at Eifel. The mineral has been found in a few localities worldwide. Very nice under the microscope. — Photo: David Hospital · CC BY-SA 4.0
Willhendersonite
Willhendersonite is an IMA-recognized mineral species in the silicate class, with the chemical formula KCa(Si₃Al₃)O₁₂·5H₂O.
It crystallizes in the triclinic crystal system (space group P-1). It is a member of the Chabazite structural group.
Key properties: Mohs hardness 3; specific gravity 2.1–2.18; Vitreous luster; optically biaxial.
IMA symbol Whd, IMA status: approved, named in 1981.
A secondary mineral formed by low-temperature hydrothermal alteration of potassic basaltic lavas (San Venanzo quarry, Italy); by contact metasomatism of limestone xenoliths in basalts (Ettringer Bellerberg volcano, Germany).
It is found associated with Phillipsite, thomsonite, apophyllite, melilite (San Venanzo quarry, Italy); gismondine, chabazite, ettringite, thaumasite, phillipsite.
The name refers to Dr. William A. Henderson, Jr. of Stamford, Connecticut, USA.