Formula: (Al, Fe, Li, Mg, MN, Ni, Zn)6 (Si, Al)4O10(OH, O)2 MONOCLINIC or TRICLINIC
Description: Chlorite represents a group of over 10 minerals related by complex solid solution substitutions. These minerals are generally fine-grained, micaceous and dark green. They are not easily distinguished except by sophisticated chemical and X-Ray analysis. The specific type of chlorite found at a particular locality is noted only where it has been reliably established in the literature. Chlorites are most commonly formed in a wide range of low grade metamorphic environments produced by burial and regional metamorphism, hydrothermal alteration and recrystallization along faults and shear zones. It is often associated with such minerals as epidote and actinolite. It is a major component of slates, phyllites, greenstone and greenschists. Some varieties form during the primary crystallization of hydrous magmas. Chlorite may also form in soils and persist as a detrital mineral in sedimentary rocks. It is an abundant mineral in Wisconsin. Only the most remarkable or representative of the many localities in the state will be noted here.
ASHLAND COUNTY: Fine-grained chlorite is an abundant component of slate and associated rocks throughout the county. Van Hise and Irving (1892) note it in quartzite on the north side of the Bad River sec. 17 T44N R3W and near Mellen at the NE NE sec. 8 T44N R2W.
— Van Hise and Irving (1892) describe chlorite in the iron formation, from Mellen to the Marengo River. It is particularly evident in coarser veins with quartz and siderite. Laybourne (1979) reports chlorite with magnetite, talc, hematite, almandine and grunerite at Mt. Whittlesey in the SW SE sec. 9 T44N R2W. This chlorite is described as “thuringite” and iron-rich chamosite.
— Van Hise and Irving (1892) note chlorite as a component of the Bad River marble throughout the Penokee Range. Here it is associated with calcite, dolomite, quartz, tremolite, sericite and pyrite. An outcrop is under the old railroad bridge at Penokee Gap in the SE NW sec. 14 T44N R3W.
— Chlorite is common in metamorphosed Keweenawan basalts in the country, were it is associated with biotite, actinolite, albite and epidote. These rocks are widely exposed in T45N and T44N R4W (Leighton, 1954).
BAYFIELD COUNTY: Fine-grained chlorite is an abundant component of the slates throughout the county. A typical locality noted by Van Hise and Irving (1892) is near the Marengo River, SE sec. 15 T44N R5W.
— Chlorite is common in metamorphosed Keweenawan basalts in the county where it is associated with biotite, actinolite, albite and epidote. These rocks are widely exposed in T44N R5W and R6W (Leighton, 1954).
— Chlorite is common in the amygdules and groundmass of Kewenawan metabasalt exposed in the south half of sections 4 and 5 T44N R6W south of Grandview. Associated minerals are quartz (variety agate), epidote, K feldspar, pumpellyite and bornite (WSC Field Notes, 1990).
— Chlorite is found in the Keweenawan metabasalts in the pits and shaft of the Melrose copper prospect, NW NW sec. 12 T44N R9W (Grant, 1901). Here it is associated with prehnite, copper, epidote, calcite, quartz and laumontite.
CHIPPEWA COUNTY: Chlorite with kaolinite is a major component of the regolith at the contact between the Mt. Simon sandstone and the underlying Precambrian trondhjemites along Duncan Creek in Irvine Park, Chippewa Falls (Cummings and Scrivner, 1980).
CLARK COUNTY: Chlorite is a common component of the kink-banded quartzite and chlorite-muscovite schist in a quarry along the South Fork of the Eau Claire River on County M in the NE sec. 1 T26N R4W (Myers, 1977; WGNHS Outcrop Descriptions).
DOUGLAS COUNTY: Chlorite is widespread in the amygdules and groundmass of the Keweenawan metabasalts throughout the county. Irving and Van Hise (1892) report chlorite as associated with prehnite in the NW sec 2 T.44N. R.13W. and in large amygdules in the SW sec. 6. T.44N. R.13W.
— Chlorite is an abundant amygdule mineral with prehnite, calcite, quartz, chalcopyrite and K feldspar in metabasalt in the quarry in the NW NW sec. 1 T47N R13W (Cordua, 1990).
— Fine-grained dark green chlorite forms in veins and amygdules with copper, epidote and calcite at the F Shaft of the Weyerhauser Mine, SE SE sec. 11 T43N R10W (WSC Field Notes, 1990).
— Dark green chlorite forms in amygdules, veins and groundmass in Keweenawan basalt at the main shaft of the Weyerhauser Mine, NW SE sec. 12 T43N R10W (WSC Field Notes, 1990).
FLORENCE COUNTY: Iron-rich chlorite with an x-ray patter similar to thuringite is found at Keyes Lake in massive chlorite rock, in veins and as metacrysts in surrounding rocks. Associated minerals are garnet, tourmaline, biotite, magnetite, pyrite and stilpnomelane (LaBerge, 1960).
— Small chlorite porphyroblasts are common throughout the Michigamme slate where it is associated with graphite, magnetite and siderite. Some specific localities are on the south side of sec. 32 T40N R18E and in the NW sec 6 T39N R18E (Dutton, 1971).
— Chlorite is a component of the stilpnomelane-rich quartzite found in sec. 31 and sec. 32 T40N R18E. Associated minerals are garnet and a fibrous yellow amphibole (Dutton, 1971).
FOREST COUNTY: Chlorite is a major component of the country rock as a metamorphic and wall rock alteration mineral at the Crandon ore body. Dark green chlorite is found with chalcopyrite in quartz veins in the footwall sequence (May and Schmidt, 1982; Lambe and Rowe, 1989).
IRON COUNTY: Chlorite is abundant in the iron formation of associated rocks of the Gogebic Iron Range throughout the county. It occurs in the groundmass and in cross-cutting veins with quartz and siderite. Some localities are at the Germania Mine in sec. 24 T46N R2E and along Tyler’s Fork in sec. 34 T45N R1W (Irving and Van Hise, 1892). Laybourn (1979) describes chlorite associated with magnetite, hematite, dolomite, stilpnomelane and minnesotaite along Tyler’s Fork in the SE NE sec. 33 T45N R1W.
— Chlorite, associated with tourmaline, is a common accessory of gneisses in sec. 5 T44N R1W (Van Hise and Irving, 1892).
JACKSON COUNTY: Common throughout the rock of the Jackson County iron mine, east of Black River Falls in the SE sec. 15 T21N R3W. It is particularly common in the talc schist that form both the hanging wall and foot walls of the ore body. It is a relatively late-formed mineral found in coarse masses intergrown with talc, various amphiboles and magnetite. It partially replaces other minerals, particularly almandine (Jones, 1978; WSC Field Notes).
MARATHON COUNTY: Masses up to 1-3 cm in diameter are found in pegmatite and throughout sheared tonalites in the roadcuts south of Marathon in the SW NW sec. 18 T28N R6E (WGNHS Outcrop Description).
— Abundant in clays and as tiny granular crystals in pockets in the pegmatites of the Wausau pluton, such as is exposed in the rotten granite quarries south of Rib Mountain in sec. 19 and sec. 20 T28N R7E (Falster, 1987).
MARINETTE COUNTY: Chlorite is abundant in the rocks of the Quinessec volcanics throughout the county where it is associated with epidote and actinolite. A typical locality is in the center of sec. 1 T37N R20E along Hwy 141 north of Pembine (Inst. Lake Superior Geology, 1973).
— Chlorite occurs in groundmass and amygdules in pillow basalt exposed in the quarry at Kremlin where it is associated with epidote, actinolite and stilpnomelane (Depangher, 1982).
OCONTO COUNTY: Chlorite occurs widely in metavolcanic rocks near Mountain. (Sims et al., 1991).
ONEIDA COUNTY: Chlorite is a component of mafic pillow basalt on the east edge of Monico in the intersection of US Hwy 8 and County Road V in the center of sec. 29 T36N R11E (Mudrey, 1979).
Found lining amygdules in andesitic pillow lava in and around a gravel pit north of Monico in NE NE sec. 30 T36N R11E (Mudrey, 1979).
POLK COUNTY: Chlorite is widespread in amygdules, along joints and in the groundmass in the Keweenawan basalts found throughout the county. One locality is at the Dresser Trap Rock Quarry in sec. 5 and sec. 6 T33N R18W. Here it is associated with epidote, actinolite and hematite (Cordua, 1989b).
PRICE COUNTY: Chlorite occurs in the metavolcanic rocks of the Ritchie Creek massive sulfide deposit (DeMatties, 1990).
RUSK COUNTY: Common component of schists associated with sericite. andalusite, biotite, quartz and spessartine in the Flambeau Copper Mine south of Ladysmith (May, 1977).
SAUK COUNTY: Common component of the iron formation at the Illinois Mine 3 miles southwest of Freedom and elsewhere on the Baraboo Iron Range (Leith, 1904). It is also common in the phyllites within and overlying the Baraboo Quartzite (Geiger, 1986).
SHAWANO COUNTY: Dark green chlorite is a component of the beryl-bearing pegmatite exposed along the Embarass River south of the Tigerton Dells in the NE SW NE sec. 15 T26N R12E (WGNHS Files, 1986).
WOOD COUNTY: Component of talc schist and tremolite schist in the Milladore talc mines such as the Trowbridge-Nott mine in the SW NW sec. 11 and the Something Mine NE SW sec. 15, both in T25N R5E (US Bureau of Mines, 1963).
— Found in quartz veins with anatase and quartz xls. in the Tork Company Quarry, and Hassely Quarry in Wisconsin Rapids (T Buchholz pers. comm., 1993).
— As coatings and tiny crystals in vugs in red granite at the Fredreich Schill Quarry, NE of Vesper on the east side of Hwy 180 (Buchholz, 1994 pres. comm.).
— Occurs as thick coatings along faults and joint surfaces in granite at the John Cepress Quarry, sec. 11 T.27N. R.2E.
— Chlorite occurs masses along joint and fault surfaces and as fillings (chamosite?) in miarolitic cavities in granite at the Haske Quarry, sec. 25, T24N R2E. (Tom Buchholz, et. al., 1998.).