Surface of diabase matrix coated with white needle-like natrolite crystals. Horseshoe Dam, Maricopa County, Arizona. Field of view about 10 cm left to right. (Photo by W. Cordua.)

Formula: Na2Al2Si3O10.2H2O Orthorhombic


Natrolite is a member of the zeolite family that occurs most frequently in veins and as amygdule fillings in basaltic rocks.

BAYFIELD COUNTY: Thin veins of coarsely fibrous radiating clusters of white natrolite cut amygduloidal basalts in roadcut along Hwy 27 NE SE Sec. 32 T.44N R.9W (WSC field notes).
Natrolite is found in amygdules in basalt in the SE SW Sec. 4 T.44N R.6W; the NW SE Sec. 5 T.44N R.6W and the SE SE Sec. 36 T.45N R.6W near Grandview (LaPoint, 1976).

DOUGLAS COUNTY: Natrolite was tentatively identified in thin veinlets with phillipsite (?) and calcite in gouge cutting basalt along the Douglas Fault exposed along the Amnicon River in Amnicon Falls State Park (SE Sec. 29 T.48N R.12W ) (Ludvigson and Anderson, 1986).
— Thin white natrolite xls. up to 5 mm occur along joint surfaces in gabbro at the Buckley Quarry, SE NW Sec. 32 T.48N R.12W south of Hwy. 2, near Amnicon Falls (Cordua, 1991).

IRON COUNTY: Coarse radiating groups of natrolite has been identified in amygdule fillings in flow tops of the Porcupine Volcanics exposed along the Montreal River at Saxon Flowage. The identification was verified by XRD and energy dispersive x-ray analyses. (W. Cordua, 2014 personal notes).

MARATHON COUNTY: Natrolite occurs as an alteration product in rocks of the Stettin pluton, near Wausau. (Falster, et al., 2000).