Apatite Group

Botryoidal carbonate-rich apatite on massive carbonate-rich apatite matrix. Field of view is about 3 cm left to right. From the Flambeau Mine in Ladysmith, Rusk County, Wisconsin. (Photo by Pete Rodewald.)

Formula: Ca5(PO4)3(F,Cl,OH) Hexagonal


Apatite denotes a family of minerals referred to variously in older literature as “fluorapatite,” “chlorapatite,” “carbonate-apatite” or “hydroxlyapatite” and in newer literature as apatite- (CaF) etc. depending on which anion group dominates. Members of the family can occur in a wide variety of environments, usually as small accessory mineral grains. It is found in small amounts in virtually all igneous rocks. Coarse apatite may be found in pegmatites. Metamorphic rocks also commonly contain apatite in tiny grains. Large attractive apatite crystals may occur in marble. The mineral forms detrietal mineral in sediments. It may also be chemically deposited, often as carbonate-bearing varieties in sedimentary rocks. Shell fragments of inarticulate brachiopods and other fossils are formed by carbonate apatite. These sedimentary apatites are widespread in the Paleozoic rocks in the state. Since many literature references do not specify the particular member of the apatite family found at a given locality, all apatite occurrences are grouped together with the specific apatite mineral noted where known.

ASHLAND COUNTY: Irving (1883) notes tiny apatite grains as a common component of the chlorite hornblende gneisses from Penokee Gap. Apatite forms up to 2.6% of the monozogabbro of the East Mellen complex in NE 1/4 SW1/4 Sec. 23 T.45N. R.2W. (Tabet and Mangham, 1978).
— Apatite is a common accessory in the Mineral Lake Intrusion where some rich cumulate layers may form, especially in the ferrodiorite zone toward the top of the pluton (Klewin et al., 1989).

BROWN COUNTY: Oolites and concretions of apatite up to 1.25 cm in diameter occur at Katell’s Falls, east of DePere, SE NE Sec.32 T.23N R.21E (Paull and Emerick, 1991).

CLARK COUNTY: Apatite occurs in small crystals in amphibolite the Long Branch Quarry west of Thorpe. These fluoresce yellow under shortwave ultraviolet light. (Tom Buchholz, pers. com.)

DODGE COUNTY: Carbonate apatite occurs in colorless fibrous and yellowish to bluish concretionary material in the oolitic Mayville iron ore (Hawley and Beavan, 1931).
— Tiny red hexagonal plates of apatite were found in quartz veins and pegmatites cutting quartzite in the Michels Materials Waterloo Quarry, NE sec. 33 and NW sec. 34 T.9N. R.13E. (Buchholz et al., 2003)

DUNN COUNTY: Apatite forms phosphatic shell fragments in the Eau Claire and Mt. Simon formations. A typical locality is in a roadcut on County H, 1 mile north of the Chippewa River near Caryville (W.S. Cordua field notes).

FLORENCE COUNTY: Apatite forms tan to light brown nodules up to 3 meters in diameter with rims of lithiophyllite and fillowite in a zoned lithium-rich pegmatite “in Florence County” (Falster, Simmons and Moore, 1988). Work at the Red Ace pegmatite verifies manganapatite there (Falster et al., 2000).

GRANT COUNTY: Carbonate apatite is widespread as tiny nodules and as phosphatic fossil material with the Platteville and Maquoketa formation in the Rewey-Mifflin areas and elsewhere in the county (Taylor, 1964). Such nodules found abundantly in a lower part of the Pecatonia Member of the Platteville Formation found in roadcuts on County N in SE NE Sec. 19 T.4N R.3W (WGNHS outcrop ). Apatite nodules in the Glenwood and Platteville Formation exposed in the Hoadley Hill roadcuts along US 151 SW of Platteville in the NW NW Sec. 12 T.2N R.2W (Mudrey, 1978).

IRON COUNTY: Apatite is common as microcrystals in the Keweenawan gabbros of the Gogebic iron range (Van Hise and Irving, 1892).

JACKSON COUNTY: Fluorapatite reported as a component of phosphatic brachiopod shells in the Eau Claire Formation at Castle Mound, SW Sec. 24 T.21N R.4W, just west of US 12 on Castle Mound Road Apatite is also a component of shells in Lone Rock Formation in same region. An exposure is in the burrow pit on south side of Pine Creek Road in NW Sec. 10 T.21N. R.5W An apatite-rich brachiopod hash in the Mt. Simon is exposed in a roadcut on Moss Hill Road, NW Sec. 29 T.21N. R.4W (Klemic and Ohlson, 1973).

LAFAYETTE COUNTY: Apatite is a common component of phosphatic nodules and in the Maquoketa Shale in the Belmont and Calamine Quadrangles, especially in the depauperate fauna zone at the base of the unit (Klemic and West, 1964). Carbonate apatite also occurs in tiny nodules 1 mm to 1 cm in maximum diameter within the Pecatonia member of the Platteville Formation through these districts, and, likely, throughout the region (Klemic and West, 1964).

MARATHON COUNTY: Apatite is a widespread constituent of the igneous rocks of the Wausau region (Weidman, 1904a). Sood et. al., (1980) note it particularly as a component of the rim and core zones of the Stettin pluton such as in SW 1/4 Sec.2 and the SE 1/4 SE 1/4 Sec.22 T.29N R.6E. Falster (1987) and Buchholz, Falster and Simons (1999) describe fluorapatite as small crystals up to 12 mm long within cavities in the pegmatites of Wausau pluton. These crystals are colorless to white and fluoresce cream to tan in shortwave ultraviolet light. These pegmatites are exposed in the “rotten granite” quarries, such as south of Rib Mountain in Sec. 19 and 20 T.28N R.7E. (Falster, et al., 2000).
— Fluorapatite occurs as clear to white micro-xls. at the Koss Pit (SW sec. 2 T27N R.5E), the Red Rock Granite North Pit (along Spring Brook Road), the Ladick Quarry (sec. 19 and 20 T. 27N. R.6E.) and the Wimmer #3 pit (NW sec. 19 T.28N R7E) (Buchholz and Simons, 2002).
— As tiny crystals with aegirine and garnet in syenite at Old Thorium Mine Stettin (Buchholz, 1994, personal communication).

POLK COUNTY: Carbonate apatite forms a major component of the phosphatic shell fragments in the Eau Claire and Lone Rock Formations, such as exposed in Interstate Park south of Eagle Peak in the SE 1/4 Sec. 36 T.34N R.19W (W. S. Cordua, field notes).

PORTAGE COUNTY: Widespread accessory in the granitic rocks of the Wolf River Batholith (Greenberg et al., 1986).

SAUK COUNTY: Small crystals of clear fluorapatite occur in a glacial erratic granite boulder found in the Jesse Pit, near Baraboo, WI NW Sw sec. 15 T.11N. R.7E. Associated minerlas include anatase, fluorite, zircon and unidentified thorium and LREE-carbonate minerals. (Buchholz, 2003)

TREMPEALEAU COUNTY: Common as brachiopod shell material in the Eau Claire and Wonewoc Formation at the Bruce Valley Quarry (NE NW Sec. 9 T.23N. R.8W) (WGNHS outcrop description).

WAUPACA COUNTY: Widespread accessory in the granitic rocks along the Wolf River Batholith (Greenberg et al., 1986).

WOOD COUNTY: Apatite occurs as “small white to clear rounded hexagonal prisms and sometimes as bluish to greenish translucent crystals and masses near and in pyrite” in the Tork and Haessley Quarries, near Wisconsin Rapids. The apatite fluoresces yellow under shortwave ultraviolet light (Buchholz, 1996).